Ammonia in Bettas tank

Question
Hi Darryl,
I have a Betta fish in a 10 gallon tank. A pair of weeks ago I added two Mollies, to make him happy and have some company. Contrarily, he did not like them and I take them out of his tank. Since them I have been fighting with the ammonia level. I have changed the filter and made several water changes (30% each). Now, the ammonia level has decreased, but there is still a little bit. Also, Betta's tail does not look 100% ok. What should I do? Make another water change? Take the filter out and put some medication?
In this case which one? The last time I changed the water was yesterday. Thanks.

Answer
Hey Maria,

Mollies are typically not a good choice for a tankmate with long fin, slow moving fish. Mollies can at times be very, very aggressive. If you want to have suitable tank mates, wait a few weeks (3-4) and get some tetra. Betta typically leave them alone, and tetra are regarded as completely nonaggressive.

As for the current water problems, I'd simply get a small bottle of AmQuel plus. A bottle for 60 gallons is something like $2.99 (USD). I would not recommend changing the filter media for atleast a week, on the grounds that the beneficial bacteria that process ammonia into nitrate typically attach to the filter cartridges. The AmQuel will really help settle things though. As for the fins, it's possible the mollies just nipped at them, and I'd just watch them for a day or so. If they continue to get worse, yes, treat them with an anti-fin rot medication. If they stop getting worse, then just give him some time to recoupe.

Hope this helps! best wishes.