tank won't support alk

[Fishmommy]

at my wits end.
my alk, no matter what I do, levels out at around 6.5 dKH.
I can add alk up to 7.5 at night, but by the next afternoon it is back to 6.5.
I removed my sand, hooked up a CO2 scrubber, and am dosing mag like crazy.
pH runs around 8.2.

I dose alk a few minutes on the hour with my apex, and dose a few minutes of cal on the half hours.

I have been trying a mega bolus of alk each night to bring it up but by next day it is back down despite my regular dosing supposedly keeping things fed in the tank.

aaaaaaaaaargh. It has been like this from the beginning. I my sand was turning to rock due to precipitation so I removed it but it is still going somewhere! How can I stop this?

I am going through gallons of alk and my corals are not growing.

[Sk8r]

If your magnesium is low, alk can't be raised. There are two possibilities---that your magnesium is under 1200, or that your alk test is expired and not reading right, which can lead to a real mess in the pipes (ask me how I know.) First check the mg.

[tylersarah]

do you run gfo?

[Fishmommy]

I use a hanna checker colorimeter for alk. I can use a new bottle of green stuff with it or do you think the colorimeter device itself is suspect?
My mag is above 1600 .. Red sea tester for that. I do dose mag a lot.

I do run a gfo reactor. When my mag gets below 1400 it precipitates calcium in the gfo but currently not an issue. Why ask about the gfo?

[E Rosewater]

Also, depending on how the Alk is being added, if it's a large amount at once precipitation of Calcium Carbonate could be occurring due to a localized pH drop.

[Fishmommy]

I dose alk at a rate of 1.1 ml per minute for a few minute an hour around the clock. Recently I have added bolus doses of 50ml all at once in addition to the regular dosing. The bolus raises my pH a bit, and after an hour I test alk and life is good, but by the next day I am back,where,I started.

[outssider]

Also, depending on how the Alk is being added, if it's a large amount at once precipitation of Calcium Carbonate could be occurring due to a localized pH drop.

+1 except you have it wrong, the ph is rising not dropping...

switch from sodium carbonate to sodium bicarbonate. the bicarbonate won't raise the ph and you will stop precipitating calcium carbonate all over the place ...

[Fishmommy]

I am listening and may try that. It confuses me though because lots of people dose soda ash but don't have the problems I am having. What is it about my system that makes it precipitate? I use RODI and monitor TDS, I dose soda ash at least 20 minutes away from calcium, I keep my mag high.....why can't I have a stable alk like regular folks? I dose alk at a low rate except for these past two days.....*throws tantrum on the floor*. Lol.

[dkeller_nc]

The first thing to do is to check your alkalinity test, preferably with another test brand. Many folks have reported issues with the hanna checker alkalinity test.

I'd suggest Salifert because they're inexpensive and contain a known standard alk solution to help you interpret the end-point. But a Red Sea Pro or even an API kit if you have it on hand will give you a reality check.

In my hands, Red Sea Pro Mg tests reports high values by about 200 ppm. I checked it by making up a lab standard for Mg, same result. So it's at least possible that your Mg is lower than you think.

With respect to soda ash vs. baking soda, it's possible that the local pH rise in the sump compartment is promoting precipitation. As an easy test, I'd switch the dosing location to the tank itself and see if the precipitation problem doesn't improve.

[Fishmommy]

Will do both.

[E Rosewater]

+1 except you have it wrong, the ph is rising not dropping...


Yeah, I can't believe I made that error. I should have said spike.

[bertoni]

How much alkalinity are you actually dosing? I'm not clear on that.

[Fishmommy]

Right now I am dosing 100ml per day soda ash 2 part. That supports alk 6.5. Yesterday I dosed a bolus of 100ml in addition. Alk measured 7.5 after an hour but 6.5 the next day.
Up until 2 months ago I was dosing about 200ml per day to keep it at 7.5 but everyone here said that was too much. I removed my sandbed at that point and cut alk dosing in half. Alk dropped to 6.5 and stabilized there.
System volume is 150 gallons. Tank contains lps and a few sps frags only.

[Forum Admin.]

I have run into this same issue, check your salinity. Make sure your refractometer is properly calibrated and compare results with at least 2 others. My low salinity was due to an over active skimmer and a sludged up float switch!

[tylersarah]

I had a very similar problem for years until I took GFO offline, now I don't need to constantly test alk to ensure it won't dip below 7 dKH. Worth a shot...

[bertoni]

For a 150 gallon tank, 100 ml isn't all that much, depending on exactly which supplement you are dosing. Assuming 100 gallons of actual water volume and that you're dosing the BRS chemicals, that's only about 1.5 dKH per day. My soft coral tanks went through about twice that amount per day due to coralline algae growth.

You could switch to baking soda for a few days, to see whether that reduces the consumption. The low pH of baking soda can reduce any abiotic precipitation that's happening.

[Reefstarter2]

+1 to above not one but a couple things are off, mag is the " buffer" for all and calcium and this is one of those cases where ph actually can make a difference but...... Since all and ph are related you must balance the ratio before making changes or adjustments to dosing figure about 15% less calcium than alk and mag takes a ton to bring up until it hits about 1250 give or take good luck fishmommy

[Fishmommy]

well I have the answer.
My hanna checker is off by -2dkh.
I have been chasing an alk measuring 6.5 to try to raise it but Seachem's test (which comes with a reference to double check) measures 8.5.

I tested my hanna using two different reagent bottles and got measurements of 119ppm and 123ppm. Seachem reads 150. That is a huge friggin difference.

So I have been chasing what I thought was low alk but it was really good alk.

throwing away my checker today.
thanks everyone

[Fishmommy]

and yes, 100ml isn't all that much, but I was dosing more than twice that to keep it at what I thought was 150ppm but it was actually really freaking high in reality.

learned my lesson well. trust but verify when it comes to test kits.

[Happyschneider]

before you throw anything away. Just checking that you make sure there are no air bubbles in the bottles anymore when you do the zeroing? Air bubbles can mess up the reading! Light tapping of the bottles against a table will release the bubbles. Also make sure that you wipe the outside of the bottles each time before you measure in order to remove any smears that could interfere. Finally, make sure you rinse the bottles you are using after each measurement with RODI water. I am not familiar with the Hanna alk tester but have a lot of experience with testing using lab equipment. Not saying it can't be the Hanna, as it is a very small unit but before wasting money it is worth testing that everything else is handled properly.

[Fishmommy]

I handle everything by the book but it it always possible there is some problem with my technique that I can't see. Since I got good results from the new test kit, and it has a reference to check with, this is the test kit I am gonna stick with. I clearly cannot get good results with the hanna, whether my fault or theirs, and there is no reference, so it's outta here.

[theatrus]

I've battled wonky test kits before and it's frustrating. I had an old Salifert kit which would stop titration at about 380ppm - which of course I adjusted back up to 560ppm.

If my Ca reactor drip becomes clogged or slows down (need to upgrade that setup), I can easily dose 100+ml of Alk a day with lower output on the reactor still contributing.