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Discussion Starter · #1 ·
My substrate is about three weeks in and is a mixture of compost and potting mix with a little peat, bone meal and phosphate and a gravel cap. The tank is 125g.

I have some plants in but no fish yet. The water has been getting cloudy (could be a mix of dust and tannins) so I have been changing water and waiting. Last major change was a week ago. I have a little circulation but no significant filtration yet although I have a filter brewing.

If I stare at the tank I can see many bubbles (like maybe one a second, sometimes more) coming from all over the tank, and there has been a smell developing. I am doing a large water change at the moment.

My ammonia stays around 2 or so without the filtration. pH is 7.3 and GH has come up to around 10 in the last week (my tap water is very soft).

I have been skimming a potent rainbow coloured scum from the top as it has been blocking the light, but it concerns me a little that there could be something undesirable in the soil.

I'd like to put some fish in there. I'm thinking of throwing in the filter but I can't see how that would stop the soil from doing it's business. Should I be doing anything?
 

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Fresh Fish Freak
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Yeah, get some water circulation ASAP, and do some serious water changes (I'd do at least a few 75%). Sounds like your tank is turning into a stagnant swamp with methane/CO2 coming from the organics in your substrate. You need water circulation to keep the tank from becoming anaerobic- it won't cycle till you get aerobic N-bacteria going, and you've probably got little to none of those in there with no water circulation distributing O2, especially down in your substrate.

Actually, I just noticed the word "compost" (!!!) Most compost is manure-based- and manure is much too "hot" to be used in a fish tank.

Personally, I'd tear the whole thing down and start over, and NOT put compost in a tank next time around. You also need to be sure to find potting soil that doesn't have ferts added, as those also will contribute to water quality issues. Worm castings would be a much safer substitute over manure. Or DIY some mineralized soil.

Definitely don't put any fish in there unless you can ever get the ammonia and nitrites down to 0ppm. I personally don't think that will be possible until after all the compost decomposes (perhaps a year or so? total guess on my end, depends I suppose on how much you put in there?)
 

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Discussion Starter · #4 · (Edited)
Arrrrgh!

My water change (75%) has helped, slowing the bubbles noticeably, and virtually eliminating the smell. The plants seem quite happy with all this. I've also installed a filter with good flow and I have the air injection running through it.

I've been reading again and again about things like compost in a Walstad tank, and respected members mentioning 'muck' in their tanks being a good thing and potting mix being good.

Potting mix, as I know it, contains bark chips and now I find that bark is undesirable....and may even be causing the tannin leaching.

Anyhow, I suppose I have 20% compost, 20% potting mix and 60% sand, gravel and other stuff.

I've aquascaped and I've planted, and I'm desperate to free a tank for a breeding pair of angels, is there any chance I could make this work as is?
 

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Fresh Fish Freak
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Ahhh- you're setting up an NPT- that explains a lot. :)

At this point if you want to give it a go, personally I'd just keep up with the big water changes whenever the ammonia gets up to 2.0 (as much to take care of the smell as anything else) and watch your parameters like a hawk.

If you can get to a point where the ammonia and nitrites are down and stable at 0ppm and you are still getting some nitrate readings, you might try a few hardy fish and see how it works.

I've never set up an NPT myself, but my understanding is that it's often a good idea to throw some dolomite in the substrate to help keep the pH from dropping too low (below about 6.0 N-bacteria shut down)- do you have dolomite in there?

You're braver than I! If I ever set up an NPT my first attempt will be on a much smaller tank LOL
 

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Discussion Starter · #6 ·
Umm...thank you :D

My lighting is low but it is on the medium side of low. I am intending to fertilise it if or when the plants show signs of needing it. I have a little java moss but everything else is in the soil. I imagine that the filter will grow to handle the ammonia so I may not appreciate the continuing amount of decomposition, especially if the plants can keep up with the nitrates.

No, I don't have any dolomite in there, I must have overlooked it. I wonder if it would balance the reactions and reduce the gas. With all the leeching hardness at the moment the ph seems stable. I guess I could fill a syringe or turkey baster with kalkwasser paste and inject it into the soil.
 

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I would definitely not put a breeding pair of angels in the tank. If you are going to breed angels you might want to consider a bare bottom tank with a sponge filter if you are planning to raise the spawn.
 
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