Low pH and low kH

[JerryJ]

Hi everybody,

 

I seem to have a pH problem in my 29 gallon FOWLR tank. The tank has a shallow aragonite bed, a Bak Pak protein skimmer, and an Aqua Clear power filter. The only fish is a small firefish. The tank is kept covered, and I change at least 10% of the water weekly. The tank has been in operation for about 5 months.

 

The pH and alkalinity have always been a bit on the low side, but lately the pH is dropping enough to worry me. It's about 7.7 in the morning, and 7.8 in the evening. Recently I lost a fire shrimp, and even more worrisome is the apparent effect on small critters in the sand bed, rocks, tank walls, etc. I don't see any copepods at all now.

 

Other parameters: SG 1.023, Calcium 500, alkalinity 1.7 meq/l, magnesium 1350.

 

So the calcium is high and the alkalinity is low. Is there a connection, and if so, which is cause and which is effect? Does high calcium cause carbonates to preciptate out, lowering the alkalinity and allowing the pH to go down, which dissolves calcium from the aragonite and keeps the calcium up? Something like that seems to be the case, because adding Brightwell Alkalin8.3 buffer hasn't had much effect on alkalinity or pH. I've put enough buffer in to get the alkalinity up to at least 2.5 (according to the label), yet it hasn't made much difference. Something must be removing the carbonate salts I'm putting in.

 

I thought to bring things close to where they need to be with a big water change. But when I tested my WC water, the parameters were: pH = 7.9, alkalinity = 1.7, calcium too high to measure (above 520)! Not much better than what's in the tank now.

 

I use Coralife salt. Should I conclude that my bucket of Coralife is worthless, and switch to another brand? I have the feeling Reef Crystals is sort of the gold standard in salt, and according to http://aquariumwatertesting.com/AWT_...lysis_0208.pdf it has low calcium content. If I switch to Reef Crystals, could I get in trouble due to chemical incompatibility between the Coralife and the Reef Crystals? I've heard some salt brands don't mix with others.

 

Thanks for any wisdom you can provide...

 

Jerry

[onux20]

Jerry,

I was having similar issues. Check out post number #3 in this thread. Oragami is a very smart guy and included some great articles that may shed some light on your current issue.

 

 

HTH

Ron

[OldReefer]

This is the time of year for low pH. Your low Alk isn't helping but the real culprit is high CO2 levels in the environment from having the house shut tight with the AC on. You can solve that by getting fresh air to the tank or using a CO2 scrubber.

 

As far as salt goes, I'd consider Reef Crystals or try dosing a little bit of 2 part.

[JerryJ]

OldReefer,

 

Thanks for the suggestions...what is "2 part"? Also, I've never heard of a CO2 scrubber before; what is it and where can one get such a thing?

 

Jerry

[Origami]

Hi Jerry,

Your magnesium levels are right where they should be. Calcium is high and alkalinity is low. (1.7 meq/liter = 4.76 dKH). Low alk will give you poor buffering and subject you to wider pH swings. You're not seeing big swings, though, and that could be because you're not running a full reef tank with photosynthesizing organisms that boost the pH at night. I'd advise, though, fixing your alk levels.

 

Take a look at this thread over at RC. You'll see that Coralife salt mixes up to high calcium, 560 ppm, but low alkalinity (by comparison), 9 dKH (about 3.2 meq/l). Let's assume, then, that your tank consumption has pulled that 560 ppm calcium that the salt delivers down to the 500 ppm that you're measuring. Knowing that you consume about 1 meq/liter of alk for every 20 ppm calcium, you should be down to almost no alk left and you'd be a lot harder way if this were actually the case. If I account for testing error, my gut feel is that your situation starts with the salt that you're using. It just does not provide enough alkalinity to match the very high calcium that it's giving you. Couple that with consumption in your tank and you have the situation you're describing.

 

To address this over the long haul, I would begin making the switch to something a bit more balanced. Instant Ocean or Reef Crystals may be a good place to start. However, in the near term, you need to supplement alkalinity to your tank to bring it back up over 3 meq/l (around 8.4 dKH). You can do this with baking soda.

 

To determine how much baking soda you'll need, you can use a reef chemistry calculator like this one.

 

Using 23 gallons as an estimate of your water volume, 1.7 meq/l as your starting alkalinity, and 3.0 as your desired final alkalinity, this calculator tells me that you need to add 9.5 grams (or about 2 teaspoons) of baking soda to your tank to provide the needed alkalinity boost. It also advises this caution:

 

"Dissolve it in RO/DI or distilled water before dosing and do not dose all at once. This should be slowly dosed into your aquarium. Monitor pH while dosing. Do not allow immediate impact of pH to be more than +/-0.20."

 

If you slow-drip the solution into your tank, you should be fine.

[OldReefer]

Jerry,

 

As usual Tom has all the good answers. Normally you dose a two part product (one part containing calcium and one containing part carbonate or alkalinity). Since you already have high calcium, you only need the Alk part --- which as Tom points out is really just fancy baking soda.

 

If your tank pH does not correct itself after your alk is taken back up to 9 or 10 dkh, then it is very likely there is too much CO2 around the tank. It gets worse when the house is closed up with hot weather. You can open a window, run the air intake tube for the skimmer outside, or use a CO2 scrubber.

 

http://www.bulkreefsupply.com/store/the-co2-scrubber-kit-raises-ph.html

 

I have one of these laying around the house if you would like to try it out. Get the water chemistry in line first though.

 

Good luck,

 

Bill