Had a fish tank since this summer and had some issues killing fish it was small so we got a 10 gallon tank in August. Currently we have a Betta, green Corey, and a Pleco. We had an upside down catfish and an albino Corey that unfortunately passed a few months ago. They had fin rot issues and the upside down guy was bloated.

Tonight we found the Pleco dead inside the little house. We’ve had issues with ammonia levels and this is my ‘first’ tank that i’m responsible for the water levels etc. I’ve begun twice a month partial water changes (taking about a gallon out) and was using Tetra Water Safe but now I just use Aqueon Ammonia Neutralizer as my conditioner(it suggests use as such on the label) I’m not the one that does their feeding though another household member does that (we’ve discussed not feeding them daily, everyone says not to but it’s unclear how many times a week?) Been changing the filters 1-2 times a month (I think it’s an Aqueon filter as well) Used a Jungle Fungus Clear fizzing tablet earlier this month after realizing the Fin problems may not be behind us.

How can I keep these water levels stable??
Thank you for reading.