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Hello all.

This is the first WC I've done on my tank in about a month and a half (I've been away at college and there's no one at home who can do much for it besides feed the fish and dose ferts). Anyway, I tested the water before I did a WC and the results were actually good for the length of time it had been -- nitrate was still around 25-30.

During my water change, odorless gas bubbles kept rising out of the gravel bed. This is a new phenomenon which I've noticed only since I pretty heavily planted the tank around the new year. It's not hydrogen sulfide because the tank doesn't stink to high heaven and the fish are still alive. It's possible that I actually have some bacteria which are converting the nitrate into nitrogen gas (which would help explain the low nitrates as well as the apparently harmless effects of the gas. What concerns me is that denitrification generally requires anaerobic conditions and I worry about the eventual formation of hydrogen sulfide if these conditions persist.

Has anyone experienced anything similar or have a different hypothesis for what the gas could be?

Joe Potato

Hi,
I have seen it before and I believe it is indicative of
accumulating gases from the decay of organic material.
That it has no odor is good, but you are going to want to
do the gravel vacuuming more often if possible.
Even planted, a nitrate reading of 25-30 is a little high.
Generally, a 40 indicates brewing trouble and a need
for gravel vacuuming and a water change. 30 is close.
We try to keep the nitrate down around 10 for a planted
tank.

Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

It happens occasionally in many peoples tanks, especially if you have no species that regularly disturb the gravel for you. It could just be a co2 gas pocket created by bacteria, and its not necessarily harmful. I have banjo catfish that root around, and occassionally they send up bubbles that only get disturbed in your tanks when you move things about a bit and create pressure and gaseous differences with the water change. If it smells good its not a problem. Some people just have a poke about in the gravel every few days to release the gas.

Frank, LHG, as usual your answers were informative and to the point. Thank you both.

CO2 is an obvious choice -- so obvious I didn't even have the good sense to think of it. End product of aerboic respiration, decaying organic matter because no water change for a while, large bacterial bed in the gravel... doesn't take much to connect the dots. I guess I just have a tendency to fixate on the exciting and exotic (but that's how I got my girlfriend! )

While I would like to keep the nitrate lower, my comment about how low it was actually referred to the length of time it had been since the last water change: about 7 weeks. I wish I had someone who could better care for the tank while I'm away, but unfortunately it's just not feasible. To combat problems, I keep the tank lightly stocked (10ish WCMMs, 12 corys, a few otos, and a handful of ghost shrimp in a 38 gallon) so that there isn't a major emergency while I'm at school.

I'll see if I can work with my father to get him to be able to do a WC, but he's a very "hands-on" fishkeeper; he constantly has to change things in the tank and wouldn't be content to let the system stablize. I had to bar him from doing anything to the tank apart from look at it because he overfeeds worse than an overactive 5 year old, and always says "There's room for just one more fish!". My mother is the one caring for the tank now, but unfortunately she would not be able to do the WCs.

Joe Potato

Could the food be cut down at all? The fish don't really have to be fed everyday. When I left a tank in my mom's care I had to tell her to feed once every 3days and even if you leave the tank for many weeks the fish get along fine with that. If they were only fed for 2-3days in a row and then skip a day they could live indefinitely with that feeding schedule and it might keep the tank from building up nitrates as quickly.

Already tried explaining it them, sham. The problem is that if they skip a day, they throw in twice as much food to "make up for the lost day". I figure it's better if they just feed half-as-much everyday so there's not a whole lot of uneaten food festering in it every other day.

They're dog people, so they're used to being very interactive with pets; they have trouble with the whole "Hey, let's just look at the peaceful fish tank and not play around with it" idea.

Joe Potato

It is nitrogen that becomes traped in the substrate. It is harmless, just gently stir the gravel right before your next water change and all will be well.

"There is also a Clown Pleco in this tank some where. I am telling you, HE IS IN HERE."