I asked this question a couple of month ago, I suggest you read it first so you know the context.

I have a 15 gallon tank with 10 neon tetra, 4 zebra danios, 2 endler and a bunch of red cherry shrimps (~30) fully cycled with an aquaclear 30 and a small double sponge filter. As you can see it's getting a bit cramped inside the 15 gallon so I have decided to upgrade to a 75 gallon tank. As it is, I have the 75 but don't have any other thing for it (no filtration, no heating, no lighting). Since the fish move happen at the same time as I physically move, I would like to avoid moving the population twice in less than a month.

So my question is, can a large aquarium be under filtered but also under stocked and maintain his equilibrium?


I actually made this experiment because I wanted to know and I was actually moving.

From my research, if the filtration is enough for the stocking, it should be ok in the larger tank. Sure don't try to filter a pond with an aquaclear30 but if the are really few stocking the filtration will be enough.

I my case the aquaclear30 was filtering about half the tank per hour and for the sponge I don't really know. What I'm sure is that after 3 week with no water change and the same feeding as before, the water was still pristine quality. Before I changed the water I tested it. It read like this 0 amonia, 0 nitrite and 0 nitrate. So 3 week with no water change (before I was doing 1wc every 2 week) and the filtration was holding it strong.

Do I recommend to do this? No, of course not! But if you're in a bad spot, you now know it can be done. The old heater and lighting won't be enough the do their function in the new tank so you should get replacement as soon as you can (particularly for the heater as it crucial for well being of many tropical fish).

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