Falling pH and Cloudy Water

[swbrewers]

I have a 300 gal. reef tank. Lots of rock, coral and about 12 fish. In the last few months, the water turns cloudy, milky white, and the pH drops. The pH was at 7.9. I did a water change and added reef buffer and that brought the pH back to 8.3 and carbonate hardness to 108. The water cleared up for a week and then clouded back up with a lowered pH after a week. Added more reef buffer and got the pH back to 8.3. That lasted another week. More cloudy water and a pH of 7.8 this week. Any ideas???
NO2-0.0, NO3-0.0, CA-410, PO3-<0.25, KH-150. R/O water in use, protein skimming in use.

 

[Vapour1ze]

Are you dosing kalk in top off?

 

[kurt_n]

It's a big read, but you might want to start here:

http://reefkeeping.com/issues/2006-06/rhf/index.php

Not enough info to know for sure, but it sure sounds like you've got a pH/alkalinity imbalance going on. In trying to chase a "correct" pH value, you're adding buffer which is throwing off the whole calcium/alkalinity balance in the water. The water eventually makes things right by precipitating calcium carbonate - the white cloudiness. Our tanks have a knack of reaching equilibrium with, or without, or help. The result of this precipitation makes the tank pH lower than it was before, and the "chase the pH cycle" starts over again.

Been there, done that. I tried to "fix" my pH problem early on in my tank and it took several months to straighten things out.

Best advice - assuming that what's going on here - is to just let the tank figure out where it wants to be pH-wise. Measure it at the same time every day to get a feel if it's consistent. Remember... pH will vary throughout the day naturally and will be lowest just before the lights come on, and highest just before they go off. pH can be altered short-term with buffers, but that's just short term. Shoot for a long term stable number and you'll be fine. The number itself - assuming it's above 7.7ish - isn't really that important.

 

[disc1]

The other possibility is that the cloudiness may be a bacterial bloom which will produce a lot of CO2 and drop the pH.

You said the pH was getting as low as 7.8 to 7.9? That's not too low. Stop chasing the pH numbers and figure out why your tank is clouding up.

 

[kurt_n]

Along the lines of David's thinking... how long has this tank been set up?

 

[swbrewers]

The tank has been up for about 16 months. It has always had a stable pH of 8.3. I only add kalk once a month or so. The CA level never drops below 400 and is usually around 410. Corals appear to be stressed, closed more than they should be. Haven't done anything different to trigger the cloudy water.