crushed coral for kH?

[mogurnda]

Well, now that I'm putting the output of my yeast bottle through the Via Aqua filter, the CO2 has gone up and the pH down. kH=4, pH=6.2, and the fish are looking a little mad. I was thinking about either dosing with baking soda or putting a small bag of crushed coral into the canister filter to bring the kH up a little to stabilize things. Am I asking for trouble?

[Aquafreak]

Yep you sure are, KH of 4 is perfect IMO for CO2 tanks. Crushed coral buffs up the KH very very slowly and often it's very hard to measure how much crushed coral for how long will add how much KH. If the Coral eventually raises the KH a few degrees your DIY CO2 might not be enough to push the pH down to appropriate levels again, with a KH of 4, try altering your yeast recipe a little and target for a pH of around 6.6-6.8. If it's fine don't mess with it, and IMO your KH is "fine" for DIY CO2, not too hard and enough to buffer against pH swings.

HTH

[NJ Devils Fan]

Yea, I would leave it. How do you mean the fish aren't looking happy? What are your water parameters?

[mogurnda]

ph, kH in first post. NO3 2.5, PO4 0.2. The platies spend less time being active, perky and loking for food, and more time at the surface, the loaches have gone from feeding out of my hand to pouting under their rocks for the past 2 days.

[NJ Devils Fan]

How long has the tank been established and what is the temperature?

[mogurnda]

T=78, tank has been running for 1.5 years, I've had the loaches for 2.5 years, replanted in April.

[djlen]

If those numbers are accurate, you have a dangerous amount of CO2 in your tank. kH 4 and pH 6.2 = 75ppm....much too high.
Unless you have a bunch of drift wood or root in the tank which would give you a false reading. If not, I'm surprised that your fish are only "mad".
Len

[carpguy]

I like crushed coral for low KHs but I don't think you need it. A KH of 4 should be stable. I never found DIY to be steady enough in output to be able to set a pH target -- not sure that thats a practical solution.

If you're getting that sort of output I'd try some surface disruption to gas some of it off as needed. Len is right -- if your numbers are accurate your levels are way too high… and higher KH is only going to raise the pH, not lower the CO2.

[mogurnda]

Thanks guys. I was hoping that one of you would answer. From what I read, those readings put me into a pretty unsafe place.
I do have some driftwood in the tank, though. What is it about it that throws off the pH or alkalinity measurements? The tannins? I tend to believe the readings though, because the pH was between 6.7 and 7.0 before I starting "improving" the system. kH has been rock-steady at 4.
The fish are alive, but still stressed, so I'll probably put a little venturi powerhead into the tank to offgas a little.

[djlen]

I've got a lot of wood in my tanks as well and can't rely on my pH readings to be accurate. Over time though, I have come to know my fish and how they re-act to the CO2 levels. So I know that a certain pH, even if it appears to be too low is ok and keep the CO2 regulated to that pH and no lower. This is much easier to do with a pressurized system than with DIY.
I would gas off some of the excess and when the fish tell you they are happy by their actions, remember that pH and try to keep it there.
Len

[mogurnda]

Thanks. More circulation seems to help, but I can certainly see why a person would switch to a CO2 tank. Hard to control the output of the bottle.