Help with water chemistry.

[pistolero]

I just got my tank up and running a few weeks ago after a 5 week fishless cycle.
http://www.aquariumadvice.com/forums/f15/my-cycle-log-163739.html
Went OK just one minor ph crash near the end.
This 55 gallon tank is now the home of 3 fantail goldfish and 5 small cories all of which seem happy, active, and eat well. I have changed at least 20 gallons at weekly pwc's and all seems well except I'm having trouble keeping my ph stable.
The tap water comes out at around ph 7.5. A few days after a water change I can test the tank water at 6.6-6.8. I went and got an API GH /KH liquid test kit and my water measures GH 5 and KH 2.
Today for the first time since the cycle I had a nitrite reading over zero, it's 0.5ppm, does the low ph adversely affect the BB?
So what should I do? Crushed coral? Baking soda?

 

[librarygirl]

Yes the PH crash could be affecting the BB. Do another water change to get the PH back up (er, and the nitrites down!). You may need to run a media bag or clean nylon stocking with CC in your filter. Eco23 might be the best to ask about this. Good luck and congrats on the fish! Keep an eye on parameters and do water changes as needed to keep that nitrite under .25.

 

[eco23]

I'd try leaving a glass of tap water sitting out for 24 hours and see if the pH level changes. Throwing an air stone in it can help, but isn't necessary if you don't have one.

I don't think your pH is fluctuating enough to hurt the beneficial bacteria, and I'd lean towards some other cause for the toxin spike. However if you do want to keep the pH stable, a small amount of CC works great for me. It really doesn't take much at all...I just keep a few pinches in a mesh bag in my filter of my 46. It holds it exactly at 7.4 (which is how it comes out of my tap). Without it my pH tends to crash within a week due to my kH being virtually zero.

 

[pistolero]

Thanks! I'll try crushed coral.
I'll check on the ph of aged tap water. But when I was doing the cycle it stayed pretty steady for the first 3 or 4 weeks?

 

[eco23]

Thanks! I'll try crushed coral.
I'll check on the ph of aged tap water. But when I was doing the cycle it stayed pretty steady for the first 3 or 4 weeks?

The of the biggest causes of pH drops is nitrification as the bacteria is converting the toxins. They consume the buffers in the water which hold the pH steady...and at the same time they're pumping out acidic waste. Those two things combined equal pH drops. When a tank is new there's not as much conversion happening...so the buffers aren't being consumed and the acid isn't being produced as quickly at that time. Just a possibility.

 

[pistolero]

That makes sense eco. Will need to build up buffering capacity and KH I suppose.
Did a 30 gallon water change. Parameters are ammonia 0, nitrite >0 <0.25, ph 7.2.

 

[eco23]

That makes sense eco. Will need to build up buffering capacity and KH I suppose.
Did a 30 gallon water change. Parameters are ammonia 0, nitrite >0 <0.25, ph 7.2.

Cool. As long as it's not large swings and you've got a good pwc schedule I wouldn't worry about it too much, but if you do decide to buffer it I'd definitely use a natural product like crushed coral instead of something in a can or bottle.

Sure is nice seeing yellow and blue in those first 2 tubes, isn't it?

 

[pistolero]

Sure is nice seeing yellow and blue in those first 2 tubes, isn't it?

YES! And I was getting spoiled for a couple weeks there when I'd get that every time!

 

[eco23]

YES! And I was getting spoiled for a couple weeks there when I'd get that every time!

Did you make any changes with filter media, tank decorations, fish deaths, added a bunch of new fish right before the no2 showed up, etc...?

There's got to be a reason for the spike, but as long as it isn't spiking high and you're willing to do water changes for a few days...it's not a big deal. Mini-cycles correct themselves pretty fast as long as you stay on top of them.

 

[pistolero]

Did you make any changes with filter media, tank decorations, fish deaths, added a bunch of new fish right before the no2 showed up, etc...?

No, none of the above. The last water change I did clean out the media in my AC 70 but I just swished it out in the water I removed from the tank for the change. I did go get 10 gallons of RO/DI water from a lfs and used it in my last 20 gallon water change, I had read this would be a good idea but I didn't realize at the time how soft my water is to start with. I realize now that was not a good idea, knowing my tap water is about 2 KH to start with. I think the combination of that with the first real cleaning out of the filter media may have been too much for the equilibrium of my BB related to the bioload.
I only have the three golds, one small, one medium, and the big one is 3&1/2" at most not counting tail. I got 5 peppered cories on the small side in there, too. Two of them may be 1.5", the other three are less than 1". I have three or four plots of Java moss, two small cabomba carolinia, and I just added a java fern and a bacopa carolinia yesterday. I am adding API Leaf Zone once a week after the water change and Seacham Excel once a day at the recommended dose. This weekend I plan to put 4 48" 32 watt t8 6500k bulbs over the tank.
Thank you so much for all your help!