ph problems

[freemo]

Hi can anyone help me with my ph problems. Our tank which is a orca 550 nano tank 128 lt, has had fish and corals in for 2 months now and our ph has just gone down to 7.8 from 8.2. All our other tests are fine.
Nitrate 0
Nitrite 0
Ammonia 0
Dkh 9
specific gravity 1.023
temp 23.9 C ( please note that none of the above have changed recently)
we do weekly 10% water changes religiously. we have good surface water movement and 2x 3000 lph power heads which we alternate every 6 hours or so.
We use tropic marin salt and have excellent ro water quality. We have contacted our local aquatics shop who could not help. So i would be very grateful if some could on this site. Thank you.

[sheamurai]

Well, I've read that excess C02 is usually the cause of low pH - did you add/subtract anything to the tank recently which would bump your co2 levels? Dosing calcium carbonate, or something along that line? Overfeeding?

[freemo]

we added a blue damsel fish and a fire fish on 7/01/2010. and our problems with the ph started on 13/01/2010. we haven't added anything as yet. I don't think we are over feeding. we have done quite a lot of research into all aspects of marine aquariums etc.. What do you think about us adding a buffer? Because someone else as advised us not to us one. Also i have read about the use of baking powder.

[AABatteries]

Excess CO2 can cause your pH to be higher. A lack of CO2 can cause your pH to drop. I had to open a window in the room my reef was in to help with the gas exchange. That was able to get my pH up to where it needed to be.

How long has the tank been running?

[freemo]

Our tank has been running for 2 months, so still fairly new. ill try opening a window thanks for the advise.

[jman]

same thing with opening a window here. I made a big difference! I forgot because winter came around here and i've been leaving the windows shut but after opening in a couple of hours i saw a difference

[BigMac]

Excess CO2 can cause your pH to be higher. A lack of CO2 can cause your pH to drop. I had to open a window in the room my reef was in to help with the gas exchange. That was able to get my pH up to where it needed to be.

How long has the tank been running?
CO2 combining with water makes carbonic acid... acid does not raise Ph.

I would try opening a window if you can. You may also want to add an air stone... I run an air stone if my PH drops too much from Co2 injection. This removers the excess Co2 from the water.

[freemo]

Thanks every one for your advice. The problem seems to be a build up of CO2 but all sorted now ph is back 8.2.