Low Alkilinity

[pnikiel]

I have the guys at my LFS stumped... and they're usually pretty smart.

Green hair algea appeared in my 125 reef tank. We found the alk was as little low, about 3, and cal was way high, around 700. I was dripping Kalk with an automatic topping system and supplimenting with a 2-part system.

So I stopped kalk and topped with fresh RO. I stopped the Cal part of the the parter and increased the Alk part. A week later the cal was coming down but the Alk was coming down too so I started up the Kalk again. Two weeks later now and the Cal is at 400 and the Alk is 2.5. I started up the Cal part again.

But we can't figure out why the Alk is going down instead of up. One guy thought that my skimmer may be removing the carbonates. But the other two guys said that wouldn't be the case. They suggested that I increase the Alk suppliment even more and come back in for another test next week.

Any thoughts on what's going on here?

 

[Boomer]

Well, that is pretty easy to explain. An old method for lowering the calcium is to increase the Alk, especially when there is very high calcium. You get what is called abiotic precipitaion. It goes like this;

Ca++(in water) + CO3-- (in water)==> CaCO3 ( Calcite solid or calcium carbonate. You are making limestone).

That CO3--, is part if your Alk along with HCO3-, where that is

Ca++ + 2HCO3- ==> CaCO3 + 2H+

As this CaCO3 forms, be it from this abiotic precip or from corals, coralline, etc., for each 20 ppm calcium drop in calcium it drops the Alk 1 meq/ l. This whitish solid may be collecting on the bottom as a powder, on the glass, in pumps, heaters or other areas. Although the Alk and Ca++ are now Ok, I would consider doing a very good water change and do so by siphoning off the bottom.

 

[pnikiel]

I add the suppliments and kalk to the return compartment of my sump, which is a 3-compartment box. my skimmer works in the first compartment. The fuge is in the middle. And the return pump is in the third. That's where I add everything and there is some powder, off-white in color, in that compartment. I'm guessing its from the big doses of the Alk suppliment.

So I clean it out. Do a water change to balance things out. Maybe change 40 gals out of the 125 gal system. And then what? Cut back on the Alk suppliment to avoid creating more precipate? But I'll still need to bring it up, say to about 4.0, don't you think? Should I make my kalk more concentrated?

 

[Boomer]

Just monitor the tank and add or sup and as need for Alk and calcium. Keep the calcium in the low 400's. High Ca++ gains nothing at all. There is also no need to have the Alk at 4 meq / l. 4 is the MAX Limit. In the mid 3's is best. And you do mean 4 meq / l dont' you, not 4 dkH ?

 

[pnikiel]

Thanks Boomer.