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View Full Version : Established reef. Why is DKH/ALK drop but not CA?


92reefer
07/30/2006, 12:06 PM
I have a 92 gallon reef tank that has been established for about 4 years now. I only have 2 fish (yellow tangs) and about 90lbs on live rock with some pulsing xenia and mushrooms growing.

I have Berlin filtration with a Aqua-C protein skimmer and no CA reactors. Very simple setup. I've been able to keep the tank pretty stable but over several months the dkh/ALK keeps dropping. I had a fresh WC a little while ago with Instant Ocean and had the parameters almost ideal at:

Salinity = 1.022
PH = 8.0
ALK = 8.1
CA = 390
MAG = 1180

Now about 4 months later:

Salinity = 1.022
PH = 8.0
ALK = 5.3!!!
CA = 390
MAG = 1175

The CA has remained in tact even though I haven't dosed anything at all but the dkh has dropped significantly. I used to use B-Ionic 2 part but the Salinity would gradually raise and my dkh would eventually drop just as it is now so I decided to leave it alone and see what happens..

I'm confused. I don't understand why everything else stays in check but the dkh/ALK drops. I used to try and correct the dkh by adding Kent Superbuffer but then it would take my CA readings out of whack by plunging..... I gave up trying to balance the 2 readings!!

I hope this problem looks simple to someone 'cause it's driving me nuts!!!

Billybeau1
07/30/2006, 12:31 PM
Are you saying those first set of parameters is 4 months ago ? Is that the last time you did a water change ?

All tanks consume alk. I'm not sure why your calcium is so high using IO, unless you used tap water for your water change.

You really should try to get your sg up first to at least 1.025.

You need to make sure all of your test kits are giving you proper readings.

There are some nice LFS's in your area, maybe take a sample of your water to one of them. And verify your results.

How does your tank look ? Everything healthy ?

92reefer
07/30/2006, 01:43 PM
Yeah. Last time I did a water change (32 gallons) was about 4 months ago. I know I know... but I don't have anything delicate in terms of coral and the tank does fine with larger more infrequent changes.

I'm using RO-DI water to start with and last time I added buffer to the fresh water before adding the salt mix. I then had to add Mag to bring the levels close to 1200 before adding some Kent Ca to bring the levels to about 390. You're right, IO is lower than that out of the box but I think that 390/400 CA and dkh of 7-11 is in the healthy range.

The Xenia and mushroom corals are doing just fine but my Corraline algae has decreased some and there is some other algaes starting to take root on the glass mostly. That's what prompted me to test the water. It seems that the bad algaes/corraline decreasing have singaled the declining dkh reading the last few times. Funny thing is my tank has been doing awesome with the same parameters and 32 gallon WC about every 8 months or so.... this is with no additives including the B-Ionic!

Does this make sense. Other thing is it's been pretty hot up here and the Summer tank temp hovers around 84-86 but that's been the same every year so I don't see that as the culprit.

Billybeau1
07/30/2006, 01:55 PM
Well, if you are starting to get microalgae, your phosphate levels may have increased. You need to test for that. No phosphates, no micro. Could be the problem with your macro decline.

I'd get your alk up and even your calcium to about 420 or so.

And I would definitly get your sg up to about 1.025. If you do a water change with a higher sg solution, it'll bump up all three.

Again, make sure all your test kits are OK. especially the sg. If you are really at 1.022, I think your tank will benefit from a slight increase.

DrBDC
07/30/2006, 02:58 PM
Ditto what Billbeau1 said. Rembember too that alk will drop about 2.8 dKh(1 meg/l) for every 20 ppm of calcium consumed. Thus in a typical reef tank starting at 420 ppm, if you wouldn't supplement it would never go below 340 (actually it would stop before that). Sometimes people keep dumping buffers and such to supplement just the alk part and then you see panic posts about ca levels in the 200's! Balanced 2 part supplements are already formulated to replace them in a balanced amount i.e. 1 cup of each gives that same ratio. That's why once a balanced 2 part is started, you have to ignore the urge to add more of one than the other and that includes adding other outside supplements like buffers and builders and such. Individual supplements should only be used when balancing water change fresh ASW to match the tank parameters.

92reefer
07/31/2006, 10:01 AM
Other than the water change. Is there anything that I can add right now to bump the ALK but not the CA?? I have B-Ionic 2 part, Kent Calk Mix (that I've never attempted to use) and Kent Super-Buffer as well as Turbo Calcium??

Billybeau1
07/31/2006, 10:30 AM
Since your pH is a little on the low side, you could use baked baking soda (washing soda). Dissolve it in a glass of fresh water and dump it in the sump. Use the online chemistry calculator to tell you how much and how much you can dose at a time.

http://home.comcast.net/~jdieck1/chem_calc3.html

92reefer
07/31/2006, 10:34 AM
Billy;

Will that change or mess with my CA levels?? I really don't want the CA to drop from where it's at..

Billybeau1
07/31/2006, 10:57 AM
Yes too much of an alkilinity suppliment can lower calcium, but in your case you are out of balance. If the calcium falls a little, just bump it back up with the 2 -part.

Your only looking at around 4 tsp over a few days. I doubbt you'll see much of a drop.

Just monitor your pH when dosing and dont let it change more than 2 points per dose.

92reefer
07/31/2006, 11:53 AM
OK. I'll run out and pick up some Washing Soda. Am I reading the tool right. It says about 4 teaspoons. Is that to be added each day or only 4 teaspoons total to get to the desired range?

92reefer
07/31/2006, 12:51 PM
UPDATE:

Tested the Phosphates with Salifert. ALmost NIL...looked like .03 I believe

Also tested Salinity with my Refracto..here's the problem Refracto always reads high around 1.025 while my Coralife Deep Six reads 1.022 so which is right? I guess I could take the median and assume 1.0235?

Billybeau1
07/31/2006, 12:55 PM
that means total over a few days so if you want to go 1 tsp over four days or 1 1/2 1 1/2 and 1 over three. Just watch your pH meter when you put the first dose in so it doesnt raise more than .2

If you cant find washing soda you can just buy baking soda and spread it on a cookie sheet bake it in the oven at 300 for about an hour.

Some brands of refractos measure about 1.5 higher than they are suppose to. If you have one of those brands then I would think your 1.023 figure is pretty close.

92reefer
07/31/2006, 02:31 PM
Cool. Off to the store.

Makes sense about the refractometers. I bought mine from Premium Aquatics...it's their own label. I took my measurements to the fish store and they used the plactic IO kind which they said was brand new and it measured about 3 points lower as well....1.022 as opposed to 1.025 on the refracto!

jdieck
08/03/2006, 01:18 AM
a) The IO plastic ones are usually accurate but still I will trust the refractometer more than the hydro.

b) On your calcium and alkalinity issue it is very simple. All tanks consume Alkalinity but not all consume Calcium. In your case the only organism capable of consuming calcium is the coralline algae so you are left with alkalinity consumption from the nitrification process alone and very little for the coralline. In other words given the status of what you have in your tank You will see more alkalinity than Calcium consumption over the long run.
So at the end of the day you need to keep supplementing Alkalinity in a bigger proportion than calcium so a two part additive, Kalk or a reactor will not help in your case.
I will use the baking Soda or Baking soda to keep supplementing alkalinity as needed to maintain your levels and the Turbo Calcium to adjust Calcium only when needed. Eventually you may have to test and adjust Magnesium if necessary.

c) Water changes will not only help you keep the balance but also will help dilute stuff that gets accumulated.
I take it that your bioload is rather small so I am not surprized that Phophates are not higher but algae may also indicate accumulation of Nitrates and Organics while the alge may be consumming the Phosphate at the same time so the low reading.