Ahoy hoy,
I have a 20 gallon tank running, about one month old. Already up to 14 fish everyone is great however, I have one a**hole male balloon molly who is harrassing the 3 female mollies AND the one black male lyretail molly.. I know I should get more girls to balance out but he only went more nuts when I added 2 new females. Advice? please and thank you!!!!

14 fish in a 20g tank is overstocked, do NOT get anymore! It could be that he's stressed from all of the fish traffic in there. I'd maybe try re-homing some of the fish. (Especially since the tank has only been up for a month!)

Did you let the tank go through the Nitrogen Cycle? If you haven't, you need to read up on it, because you will end up with a lot of dead fish.

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I started with 5 bloodfins and let them do the nitrate cycle. When testing yesterday the ph is comfortable, but my ammonia needs to be checked soon. (I just changed the filter for the first time). I decided to return the molly to the store, you're right I think he was all jazzed about the sudden company and competition for food. Since everyone else is so peaceful, hopefully it will be a good choice for him and the rest. So I'll just leave my 13 and hope they don't get sick from all this stress. So do you think the one inch to each gallon theory is not something to go by? What I'm up to is cutting it very close on that theory. Thank you for your advice

1" per gallon of fish is a general rule of thumb for a reason. Some fish produce more waste and you should account for and some fish grow to the same length as other fish, but may have more mass to them. Some fish are also just sensitive to water conditions so having more room makes them more comfortable and allows for some margin of error. As far as I am aware mollies get to be 3". So even going on the 1" of fish per 1 gallon you are still overstocked.

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1" of fish per gallon is not right at all. Once you put in the gravel, plants and decorations, you are down a few gallons.

It's best to stock the tank at 60-80% to make sure everyone stays happy and healthy. Remember, in the wild fish have way more space than what we keep them in.... you wouldn't want to live in a tiny one room apartment with 13 other people would you?

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