Does Fish Load Lower PH?

[BrianNY]

Calling all chemists...
So I've had this discus in a 29g hospital tank being treated for hex for 11 days. Bare bottom tank, 40% water change daily. He's back to his old self, eating great and ready to join his buddies in the 55g.

Tested the PH in both tanks. 29g 7.0 (just like the tap). 55g is down to 6.2. Same filters, I only change 25% daily in the 55g and it currently has 8 adult discus. What's up with that? The only difference in the tanks is the number of fish! But you'd think the water changes would stabalize it, right???? Apparently not

 

[_Nemo_]

What is your carbonate hardness?

 

[BrianNY]

2 or less. Oddly when this tank was first set up the PH was going in the other direction. It was as high as 7.8. I believe that was caused by the natural CO2 in the water gassing out.

I'm thinking now that the tank is truly fully established, the combination of fish and the nitrogen cycle keep working the PH down. The reason this hasn't happened in the QT tank is it's only been set up for 2 weeks and only 1 fish.

 

[loganj]

The biological processes that take place in the tank produce acid as a byproduct. Thus, the higher the bioload, the more acid is produced. With your low hardness, there isn't much buffering capacity in that water to start with so a little acid goes a long way. Low pH isn't a problem for discus though as I'm sure you know. They are perfectly happy in 6.0 water. I have a maintenance customer with a 55g FW tank. I battled the pH for several months and finally gave up trying to keep it at 7. I just let it go and it stabilized at about 6.6 and stays there all the time now. Since you're doing such large water changes with the Discus, I would probably just watch it closely and see if it will stabilize somewhere. The worst thing you can do is have the yo yo effect going where the pH is bouncing up and down.

 

[An t-iasg]

This happened to me too. I have two 5.5 gallon tanks, with one betta each, and I mix 1/2 tap water and 1/2 RO water. The pH when I do this is 7.4. (My tap water is often 8.2. Yikes!) The next day, when I test pH, it's 7 in one tank and 7.2 in the other. Sometimes they are both 7, but the pH stays stable. I thought it was due to the addition of the ammonia from the fish, even though the tanks have cycled. I also tried mixing the water a full day before a change, but the pH stayed at 7.4, and it wasn't until I put it in the tank that the pH dropped. Now that I read loganj's post, I realize that I could let it sit after mixing for a week and the pH would still only drop when the water was added to the tank!

 

[BrianNY]

I'm with you guys on this one. Since I know that swings in PH is adverse to the discus, merely doing a large water change can be harmful. Just part of the reason I've been keeping my eye on it. That being said, they do love the soft water.

The thing is I want to inject CO2 in my planted tanks eventually. I'm going to have to get the KH up to between 4 or 5 before I do this. I'll begin by experimenting with calcium carbonate in a fishless tank for a while.

 

[TankGirl]

I'll begin by experimenting with calcium carbonate in a fishless tank for a while.

I get very good results with crushed coral placed in a filter. I know that some serious planted tank folks use this method, since it is easy to do and to maintain, and it works better than when it is just sitting in the tank. Got mine from 3 out of the tap to 6.