pH low, won't raise - how much aeration?

[Scoot]

New 75g tank, 12 days since it was stocked with damsels (who have been since moved to a temporary aquarium), and I'm having real problems with pH. Its low, 7.4 to 7.8, ammonia is still off the chart. Nitrite (at .5) and nitrate (at 20) are present, but not really high for this part of the cycle.

While fish were in the tank, I used ammo-loc a few times, and Amquel+, so the ammonia present could be non-toxic. I know now that those things can screw up ammonia testing.

But the pH is really off. I've used 3 doses now of Kent's Super Buffer, and pH has actually gone down from 7.8 from the first dose.

Could this be an oxygen issue? I had a big airstone in the tank (the quad one, about 4" long), and was running it full-blast (solid 4" ribbon of bubbles).

How much aeration is needed in a tank this big?

Temp is maintained around 78F.

SG is right where it should be.

While the damsels were in there I did many small water changes (treated with tap water conditioner, temp and SG set to match the tank), probably approaching a total of 40% change over several days' time.

Again, I've moved the fish into a smaller temporary tank because I didn't want them suffering (and they were starting to stress as ammonia went up).

There a little bit of fish waste that I need to clean up, but I've been dilligent about not over-feeding.

I've got live sand (about an inch, yeah, I need 3" for DSB), and 4 small live rocks in there.

Any ideas why pH would still be so low and even dropping further? I was hoping to move the fish back in after the Nitrite peak of the cycle, but now I'm worried about the overall status of the water.

Also - one of my pieces of live rock (a branch about 8" long) has slowly been covered over with a milky-white film, smooth, sort of like a layer of rubber over it, which rubs right off with my sponge cleaner. Is that anything to be concerned about?

 

[hackteck]

if your tank is still doing a cycle i wouldnt worry about the ph till after the cycle is done

 

[jasno999]

Do me a favor and run a battery of tests on your saltwater mix before you add it to the tank. Find out what the PH of the water you are puttign into the tank is. IF it is at the right level then I would think your amonia and other thigns going on inside the tank right now are causign it to drop.

If the water yo uare putting in is ok then eventually I think everythign will be ok.

If the water goign in is at a Low PH then you need to figure out why that is.


YOu can also add crushed coral to teh sandbed to act as a buffer. I used that along with LS to setup my tank way back.

 

[Scoot]

Will do. I've checked the ammonia of the tap water a couple times, 0.50 both times. Been using tap water treatment as well - I'll check all the levels AFTER I get SG and temp set (but before dechlorinating tap water treatment).

Planning a BIG water change today - maybe 30g or so. A lot of work since I have to make 5g at a time

(update later)

pH out of the tap, after adding salt and tap water treatment/dechlorinator was actually high - about 8.4.

I did a 30% water change. pH in the tank is up to "about" 8.0 (I say about because the difference between 7.8 and 8.0 is a shade, not a hue, and it's hard for me to tell the difference.

Ammonia in the prepared replacement water was 0.5. Everythign else I tested was nil (Nitrite, Nitrate).

The tank is still 8.0+ ammonia. This is also hard to judge, its more blue-ish than the 8.0 scale, so I'm guessing its higher.

My concern about pH included aeration - how much is needed for a 75g tank? Is a HOB filter and an airstone enough?

 

[malkore]

Here's a question: have you testing Kh/Alkalinity yet? if not, you shouldn't be adding an alkalinity buffer.

a HOB and airstone should be plenty. it doesn't take much surface agitation to provide enough gas exchange to get oxygen in the water at good levels. surface agitation drives out excess CO2, which can lower pH. A low pH doesn't indicate low oxygen. fish gasping for air at the surface is an indication of low oxygen.

 

[Scoot]

The fish (before I removed them into the quarantine tank) were sitting on the bottom, gasping.

I havent' tested hardness or alkalinity - I thought those were just for reefs...