Still not good at determining if I'm overstocked.

To my knowledge, those are all small fishes, and your party seems to be pushing the limits of a 20 gallons, but not overcrowded.

Just keep an eye in the ammonia and nitrite levels with test kit to know if your biological filtration is good, and finally, run the filter at max flow. It won't hurt anything and you'll have a better oxigenation of the water.

Keep your water change routines.

Hope this helps.

In well kept aquarium NH3 or NO3 level in NOT a good indication as to whether your tank is overstock. Couple of years ago there was an article about an experiment, where he kept close to 200 tetras in small 10 gallon tank for over six months without loosing any of them.

You can increase the bioload your filteration can handle in many various ways and thus increase the number of fish without any adverse effect as the experiment indicates. But doing almost daily water changes you can keep the NO3 level to less than 10ppm.

But the question is, are these tetras happy in such a closed and crowded and enviroment. The logical answer is NO. They stress easily and thus prone diseases and stress will also lead to shorter lifespan.

The only way I know how to tell if your tank is over crowded is to watch your fish and observe them. If there are not acting natural and nothing else is wrong with your tank then it is possible that your tank is overcrowded. For example schooling fish require lot of room to move while other fish are very territorial and require even greater amount of space.

Rohn

You're right. I know that relying on nitrous levels is not enough the determine if a tank is overcrowded, but at least it will indicate of the fishes have a goos water to live in.

According to what I know, the fishes described in the first post can "fit" in that tank, but obviously, a 35 gl would be preferred.

It doesn't seem terribly overstocked to me. At least its not one of those slam dunk cases of overstocking.

One of the things people sometimes overlook though when considering stocking is the zones of your tank. You have a lower or bottom zone, a mid level, and a surface or upper level. Most fish spend most of their time in one of these levels. For instance, I have khuli loaches that stay at the bottom almost all of the time. I had danios that stayed at the surface or top thrid or so of the tank almost all the time. And I had tetras that spent almost all their time swimming in the middle of the tank.

My tank got along well because everyone had their own area. The one hitch I see with your tank is that I think most of the fish you listed are mid level swimmers. So, even though you have a 20g tank, they may only use the middle 7-8 gallons of it. Make sense? You're probably okay with bioload but that doesn't mean the fish aren't cramped.

Observation on your part is the best way to determine that.

T