Reef Central Online Community

Home Forum Here you can view your subscribed threads, work with private messages and edit your profile and preferences View New Posts View Today's Posts

Find other members Frequently Asked Questions Search Reefkeeping online magazine for marine aquarists Support our sponsors and mention Reef Central

Go Back   Reef Central Online Community > More Forums > Reefkeeping Online Magazine > Randy Holmes-Farley
Register Blogs FAQ Calendar Mark Forums Read


Thread Tools
Old 03/31/2003, 08:05 AM   #1
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408
Wfere to ask me chemistry questions

If you are interested in getting answers to most any reef tank chemistry questions, you should post the question in my reef chemistry forum here at Reef Central:

The forum that you are presently in is for questions directly relating to my articles at If I don't have any recent articles, I often don't check here for substantial periods, but I check the other forum daily.

Happy Reefing!

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 10/06/2003, 10:40 AM   #2
Dr Greg Alexander
Registered Member
Join Date: Oct 2003
Posts: 8
Ive read your Ca/ Alk articles. I am currently in zone 2. Salifert ALK reading is 8.22. My Ca is 420, after being in Zone 3 . Ive shut off my Ca/CO2 reactor., and assume I just wait . Am I correct?

Greg K. Alexander

GkAlex DC Houston

Current Tank Info: Leng Ecosystem
Dr Greg Alexander is offline   Reply With Quote
Old 10/06/2003, 11:05 AM   #3
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408
Salifert ALK reading is 8.22.

8.22 meq/L or 8.22 dKH?

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 11/10/2004, 07:04 PM   #4
Registered Member
fio1022's Avatar
Join Date: May 2004
Location: NY
Posts: 1,502
Hi Randy,
I've been using a TDS to monitor my D.I. unit to determine when to regenerate the resins.I'm getting a reading that varies btwn 4-6 ppm.At what point should I regenerate?
Thanks for all your valuable wisdom.

its all about time,space,and money

Current Tank Info: 240g,64g acrylic sump/fuge,Apex,AI Hydra52,Vortech MP40's,Reef Dynamics INS300,GEO 612,etc....
fio1022 is offline   Reply With Quote
Old 11/10/2004, 08:51 PM   #5
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408
Did it start lower? Most DI units should give 0-1 ppm when workign well, as as the TDS rises when the get shot, things go bad fast.

You might check this article:

What is TDS?

from it:

"7. If you are using a TDS or conductivity meter to monitor the performance of an RO membrane, then the measured value should drop by at least a factor of 10 from the starting tap water. So, for example, if the tap water reads 231 ppm, then the RO water should be less than 23 ppm. In many cases, it will drop much more than that. Less of a drop than a factor of 10 indicates a problem with the RO membrane.

8. If you are using a TDS or conductivity meter to monitor the performance of an RO/DI system, then the measured value should drop to near zero. Maybe 0-1 ppm. Higher values indicate that something is not functioning properly, or that the DI resin is becoming saturated and needs replacement. However, that does not necessarily mean that 2 ppm water is not OK to use. But beware that it may begin to rise fairly sharply when the resin becomes saturated. Do not agonize over 1 ppm vs. zero ppm. While pure water has a TDS well below 1 ppm, uncertainties from carbon dioxide in the air (which gets into the water and ionizes to provide some conductivity) and the TDS meter itself may yield results of 1 or 2 ppm even from pure water. "

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 04/08/2005, 03:04 PM   #6
Registered Member
aka_BigRed's Avatar
Join Date: Mar 2004
Location: St. Paul, MN
Posts: 162
I have a question about ion-selective probes (calcium from your recent article in Reefkeeping) and their raw output.

I'm working on a project to develop a DIY reef controller and I'd thought about adding a Ca probe to monitor Ca levels. From your article, the electrode puts out a variable milivolt reading based on the concentration of Ca, but do you know where I could find out the conversion factor from mV to PPM concentration? Is it a direct relationship or log scale or some strange equation? I'm having a tough time finding out the conversion factor/equation that the meters use. I also had the same question for a Nitrate probe.

Adding ORP should be easy since the readings and standard units people use are just plain milivolts. I just can't get info on the output conversion scale for other "fun" probes.


aka_BigRed is offline   Reply With Quote
Old 01/04/2006, 01:56 PM   #7
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408
I presume that this got answered in my other forum?

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 02/05/2007, 09:53 PM   #8
Registered Member
Join Date: Oct 2006
Posts: 3
Degradation of kalkwasser article

Hello Randy
I am from melbourne and have a 4 month old 180 liter reef tank.
This my first posting and hope i got it right.
Your articles are much valued and thank you.

I make kalk from ca(oH)2 powder in a 40liter trash bin. As suggested in your article you fill the trash can once in 2-3 weeks.
When and how do you add ca(OH)2, and or remove the exisiting sludge that has settled at the bottom of the trash can ?
In other words how often do you remove the sludge and add the new Ca(OH)2?.
Than you for the advice

glanka is offline   Reply With Quote
Old 02/06/2007, 03:57 PM   #9
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408

To Reef Central

This is an OK place to ask, but the chemistry forum is better:

I do not remove the sludge very often (once a year maybe). I usually add new calcium hydroxide whenever I refill it with water (I now use 2 x 44 gallon trash cans connected together). Sometimes i try to get more out of the sludge and don't refill with calcium hydroxide, but I always check the conductivity to make sure the potency is adequate.

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 05/08/2007, 09:23 AM   #10
Registered Member
Join Date: Sep 2006
Posts: 6
toxic dinos

Dr Holmes-Farley

Hello and first let me say how helpful your articles on reef chemistry have been. I've been in the hobby for 15 years and have learned more in the last year from reading your articles than in the rest combined. Its good to hear solid answers about alot of things that are often misconstrued in this hobby. I am writing today to try to get some answers on a very unusual problem i have been having with some of the tanks i maintain. Out of all the research i have done you are the only person who seems to have heard of this problem. I have been killing fish when i scrub troublesome algae off the sides of these tanks. I thought it was contamination with my equipment for the longest time. After taking a sample of this stuff to a veteran biologist up at CSU he identified it to me as Amphidinium Carterae a toxic Dinoflagellate that is capable of producing neurotoxins. I found your article on dinos doing a search and found that they don't like elevated Ph. I dosed numerous Kalk slurries, covered tank, and turned light off. I also did vigorous nutrient export using pura phoslock, polyfilters, and chemi-clean. it seemed to have worked for awhile however now with lights on and Ph back to normal its coming back. All water parameters check out well alk 3-4 meg/l cal 350-380 and Phosphate less than .03 yet this stuff still grows. It is dark brown in color and if let to grow for awhile will develop small hairlike structures on it. Coral and Coralline all do well. it only affects the fish which will go into shock breathing rapidly and darting around soon dying of asphyxiation if alot of this stuff gets into the water column. I desperately want to get rid of this stuff and cant believe that i am the first to ever encounter such a thing. I am hoping that you have heard of others having such problems and would love to hear some success stories on how they managed to eradicate this stuff. Any info or links you may have would be greatly appreciated. If you need more info or some pictures of this stuff i would gladly forward them to you. i have posted numerous threads on reef central but nobody seems to know what I'm talking about. I apologize for tracking you down like this but i am very eager to get some professional answers. Thanks in advance for your help.


Justin Erwin
Reefscapes Service Co
6489 S Xenophon St
Littleton, CO 80127
[email protected]

reefscapes4u is offline   Reply With Quote
Old 08/08/2007, 04:35 PM   #11
Premium Member
Join Date: Feb 2006
Location: Washington, DC
Posts: 57

(This post may be in the wrong location).

Not a question, but a THANKS. What a great way to teach/learn with the chemistry quiz.

nrehman is offline   Reply With Quote
Old 12/07/2007, 01:35 PM   #12
Registered Member
SCIFI_3D_zoo's Avatar
Join Date: Nov 2005
Location: Sebring, Florida
Posts: 1,081
Great resource your article.

I'm debating with somebody about IODINE. I read your article but I know what this guys comeback is gonna be. There are certain creatures that need IODINE like shrimp so they can molt, clams I thought, etc.

SCIFI_3D_zoo is offline   Reply With Quote
Old 09/18/2008, 09:29 PM   #13
Registered Member
Join Date: Apr 2004
Location: Fort lauderdale
Posts: 360
hi randy i read two of your article in reefkeeping and noticed some conflicting information. in An Improved Do-it-Yourself Two-Part
Calcium and Alkalinity Supplement System you said to add 3cups of epsom salt with 5cups of mag-flake but in Do-It-Yourself Magnesium Supplements for the Reef Aquarium you said it should be a 10:1 ratio magflake to epsom salt. im curious which one is more accurate or if it makes that much of a differnce.

Derrell Avant

Current Tank Info: 275g
derrell is offline   Reply With Quote
Old 12/26/2008, 05:04 PM   #14
Registered Member
Join Date: Oct 2008
Posts: 81
Hi Randy,

I have read your article on ORP with great interest and have a follow up question:

I have negative ORP readings on both my RODI water and reeftank water.

- 55l nanotank with lots of LR, 3 inch sandbed, a couple of a. percula, 1 c. poterri, 1 p. hepatus (i know, tank is WAY too small, but bugger is only 1 inch and will move to bigger meadows soon), 1 anemone, acropora sp., montipora sp., millepora sp., seriatopora histrix, discosoma sp., ricordea floridae, clavularia viridis, xenia sp., euphillia sp., zoanthus sp., 2 mitrax, 2 red hermits and 4 lysmata, bhergia v., various snails and polychaeta;
- 15l weir with growing c. racemosa and c. taxifolia, liverock, miracle mud, various sp. of copepods at 200lph water circulation;
- AquaMedic TurboFlotor Blue 1000 Skimmer skimming ok;
- Filtration with mousse and 1L Siporex (full of life) at 600lph;
- AquaMedic wave maker with 3 Hydor Koralia at 900lph each;
- I use RODI water and H2Ocean salt at 35ppt;

Tank readings are fine:
pH: 8.1
KH: 6.4 dKH
Ca: 430ppm
Mg: 1340ppm
BUT my ORP reads at a NEGATIVE 185mV. I use HM digital's ORP-200 meter.

Also, my RODI ORP reads at -90mV even after 24 hours of heavy oxygenation. I read Randy's article and understand that ORP issues are complex. We should however expect ORP readings of +200mV for pH7 water and would like to expect a reading of +350-400mV for a reeftank.

I am quite surprised by my reading, which has however been consistent over the past couple of months and is troubling me.

All the inhabitants of the tank seem happy, but can someone please help me throw some light on the issue? And suggest a solutions (that preferably does not use O3).

Thanks a lot.

timvdb is offline   Reply With Quote
Old 10/04/2009, 01:21 PM   #15
Premium Member
ItsMee's Avatar
Join Date: Aug 2004
Location: Los Angeles CA
Posts: 1,863
Hello! I am somewhat of a no0b when it comes to ca and alk. I have been studying Randy's articles and decided to use limewater as a means of a balanced ca and alk supplement. When I first tested, the calcium was at 340-360 ppm and alkalinity was around 6 dkh. I have no corals, but I do have a fair amount of coralline algae. I have never used any additives in this tank before (it is fairly new, but completely cycled). I decided to attempt to raise my calcium and alkalinity by adding more ca and alk via limewater per day than my coralline can consume thereby slowly increasing my levels to normal and to not use any other calcium or alkalinity additives other than limewater. I first started by replacing all my top-off water with 16 ounces a day with a concentration of 1 teaspon per gallon of water (I never use limewater older than 2 days). I test my ca and alk in the morning and at night with my PH readings. I noticed that since I drip this 16 ounces slowly at night that my PH readings do not change too much so just recently I bumped the concentration up to 2 teaspoons per gallon 16 ounces at a time.

My questions are: My calcium has increased to only 380 ppm while my alkalinity is now at 10 dkh - so my plans are working, but are these levels balanced? It seems that the calcium is a little on the low side (as I have heard is normal with Instant Ocean salt). Like I said, I am new to this and would like to get it down pat before introducing any corals. I would like confirmation that what I am doing is correct and I would also like to know where I should go from here. Should I add 20 ppm of calcium and then continue the balanced limewater, or should I only continue the balanced limewater without worry of adding anything un-balanced? It seems as if the ca and alk demands are fairly low considering how ca & alk have increased with how little limewater I have added - which makes sense if the coralline is the only consumer? Once the ca and alk are at levels which are balanced and just need to be maintained, what is the best way of going about finding a good approximation of what I should dose daily to not increase these levels, but just maintain them?

Also, I would like to thank you Randy, for the many articles you have spent the time to write as they have proven to be truly invaluable on my journey to a better reef! Thanks!

Last edited by ItsMee; 10/04/2009 at 01:31 PM. Reason: fixed some typos
ItsMee is offline   Reply With Quote
Old 10/05/2009, 02:50 PM   #16
Premium Member
ItsMee's Avatar
Join Date: Aug 2004
Location: Los Angeles CA
Posts: 1,863
My apologies, I really didn't mean to post the above to this sticky. I could have sworn I clicked the link before posting. I am so sorry. Please feel free to erase this post as well as the one I posted above it!

ItsMee is offline   Reply With Quote
Old 06/30/2010, 12:58 PM   #17
Registered Member
Join Date: Jun 2010
Location: M'boro, TN
Posts: 6
hi randy,

first i want to say that your articles have been very informative and i appreciate the scientific approach to explanation versus speculation and advertising.

i have a question about calcium, alk, and magnesium. we've got a 3 month old (in our care) reef tank that we purchased as an established, yet neglected, fish only tank (the owner had around 1 year i believe). the nitrates were off the charts, and we had no clue about alkalinity or magnesium testing for the first month or two.

i've been doing a lot of reading and research in the last few months (i built my own overflow and sump for a 75g display tank with 55g sump), and recently it's come to my attention via a LFS in the area that our Mg levels are low (about 750ppm), however our Ca2+ levels are around 440ppm and our KH as tested by our API test kit is coming out consistently between 17 and 20.

we recently started dosing limewater within the last 3 weeks after reading an article of yours on limewater and verifing that information across multiple sources.

we're now concerned about our KH values (however they seem balanced per your chart in .... hence my confusion

the API test kit, and the LFS suggest that our KH value is too high and is probably related to low Mg levels. my girlfriend suspects that the limewater may be precipating the Ca2+ out of our water column, however i've not seen any "snowing", and i suspect that things are ok with the drip procedure i've been using for the limewater dosing overnight. i understand low Mg levels, but how can KH be too high??

since starting the dosing with the limewater for makeup water, we've noticed an increase in coralline algae, and it would appear that our frogspawn and blue ridge coral are doing better now... however, with our lack of experience i understand that it could also be coincidental.

our most recent water parameters:

pH ... 8.3
SG ... 1.026
Ca2+ ... 460
Mg ... 750
dKH ... 18
PO4 ... 0.5
NO3 ... 20 (elevated due to recently purchased valencienna goby stirring up the sand bed? normally around 8 or so)
NH3+NH4 ... 0

can you please clear my confusion on our KH values? ...our low Mg levels? ...and possibly clear up some of the concerns with dosing limewater (will it precipitate Mg and Ca2+ if it's "dripped too fast")? ... could the limewater be binding the Mg ions and lowering their availability to the system, and if so is that a problem?

the LFS in our area also recently advised dosing with PurpleUp. what are your thoughts on this product?

lastly, we have been a little neglect in our water change routine... we only had one or two KH tests since before our last water change about 3 or 4 weeks ago, and it was reading about 14 dKH...

i just came across this article ( )of yours after more research before finalizing my thoughts/questions, and it appears we're in zone 1. does this make sense? and so we'd just stop what we're adding and leave it alone? except maybe some Mg??

sandrsReef is offline   Reply With Quote
Old 04/10/2011, 08:50 PM   #18
Registered Member
Join Date: Jul 2007
Location: altamonte springs fl
Posts: 562
best way to safly lower alk

i have a cacium reactor and been fighting my levels i cant seem to get my calcium above 300 with mag above 1300 and my alk was low so i used a alk buffer now my alk is way to high 19dkh. did a 20% water change today gonna do another i a couple of days any suggestions on how to lower my alk

skippy823 is offline   Reply With Quote
Old 04/15/2011, 12:17 PM   #19
Randy Holmes-Farley
Reef Chemist
Randy Holmes-Farley's Avatar
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 86,408
You cannot use a CaCO3/CO2 reactor to boost calcium or else alkalinity will get too high. Use calcium chloride for that.

This has more:

Solving Calcium and Alkalinity Problems

Randy Holmes-Farley

Current Tank Info: 120 mixed reef
Randy Holmes-Farley is offline   Reply With Quote
Old 08/01/2011, 07:22 AM   #20
Registered Member
Join Date: Oct 2010
Location: granada hills
Posts: 789
Hi Randy,

This question is in regards to you article about nitrite. I am about to get a 4" purple tang and have a ht for him that has the correct amount of cupramine in it. It's been running for a while but the water is a little green. No ammonia is present but there is nitrite present. Not having the API chart in front of me i believe the level is at 1. Based on the article it should be safe to place him in there right? This tank has been running for more than month. I haven't been testing it every week but it hasn't gone down to zero. I have been dropping food in every couple of days to keep the cycle going.

240 fo
180 shallow shark tank
prius and 94t supra - who woulda thought?
enjetek is offline   Reply With Quote
Old 04/08/2012, 11:47 PM   #21
Registered Member
coralsurfer's Avatar
Join Date: Apr 2011
Posts: 21
Hi Randy, I have spent several days now reading and studying up on some of your articles, and most recently you have spoken to my wife regarding her Nitrate issue.
Tonight I was reaquascaping to make room for some new additions to my reef and noticed some black algea in my front corner. It looked like mold.
I recently had a beautiful zoa rock that parished and it was in this area of the tank.
Any thoughts?

coralsurfer is offline   Reply With Quote
Old 06/06/2012, 01:45 PM   #22
Registered Member
Join Date: Jul 2009
Location: Virginia Beach
Posts: 6,655
Randy, Ive hoping to hear your input on this thread I started. You usally pop right in on alot of stuff, especially recently.

This has to do with a new product that seems to be getting heavily stocked on store shelves.......Splashless bleach. If you could tell me your thoughts, Id like to hear them

sponger0 is offline   Reply With Quote
Old 07/06/2012, 03:22 PM   #23
Registered Member
Join Date: Jan 2012
Location: Canoga park
Posts: 26
I need ell with understanding why my Rodi unit is producing water that has .09 ppm phosphates. My tds meter is showing 000, and I have a good reading showing my psi is at 60. Today I let my Rodi unit run for 40 min to let it flush out well, and I will test once more when I get home. I am using red sea and Hanna test kits. I was thinking if letting it run for 40 min doesnt work, do you think I should change the filters? Also I have a spectrapure max.

newguy88 is offline   Reply With Quote
Old 07/18/2012, 11:35 AM   #24
Registered Member
frothyspoon's Avatar
Join Date: Oct 2011
Location: Paradise Valley, AZ
Posts: 128
Hey I have been reading about peroxide dosing and am wondering whether I should use it or not. I have a ton of green hair algae on my rock that I can't get rid of and found some forums about peroxide dosing. I was wondering what other things it would kill if i put it directly in my tank since I have LPS, SPS, and some softies and also have a fuge with macroalgaes. I have a few fish along with a cleaner shrimp, an urchin and other inverts. Will dosing my whole tank hurt anything and if so, would dipping some of the rock in solution outside of the tank be fine? Any information would be great. Thanks.

frothyspoon is offline   Reply With Quote
Old 02/09/2013, 11:36 PM   #25
Registered Member
Join Date: Dec 2012
Location: Minneapolis, MN
Posts: 404
please delete

please delete

Last edited by duganderson; 02/09/2013 at 11:44 PM.
duganderson is offline   Reply With Quote

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump

All times are GMT -6. The time now is 05:01 PM.

TapaTalk Enabled

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2016 Axivo Inc.
Use of this web site is subject to the terms and conditions described in the user agreement.
Reef CentralTM Reef Central, LLC. Copyright 1999-2014