So I had an emergency which required me to move my 40 gallon fish buddies into smaller tanks with other fish. One of the tanks I filled with fish I had actually bought for it but was just scared of adding them. They do wonderful and are staying. Another tank I know is horribly overstocked and has stocking issues. However I've been doing daily water tests and so far the levels haven't been an issue at all. And ontop of that this mixture of fish is the happiest I've seen all these fish (they're actually fish from 4 different tanks that slowly all ended up together for various reasons) It's a 10 gallon tank Parameters are; Ammonia 0 Nitrites 0 Nitrates typically 10-20 (has been 20 more often with the addition of the new fish) but I'm currently doing an experiment for my plants and am going to maintain it at 5 pH 7.8 (I know this is an issue for all my tanks but my fish have adapted and are perfectly fine) My filter is for a 20 gallon tank and I do at least a 25% water change once a week, and test in the middle of the week to see if I need to do another water change or not. I just put an airstone light combo in it It's also lightly planted and once I can figure out how to properly take care of plants I will be adding more to help keep my levels maintained The stocking which I know has all sorts of issues is as follows. 5 black bellied limia (original tanks inhabitants - it was supposed to be a species only tank) 1 male betta (has never flared or chased or even followed another fish too closely the entire time I've had him he is 100% safe and I trust him with everyone in there) 3 Platies (these were from the emergency and are the biggest issue of overstocking in the tank) 6 least killifish (these were added last because they were in a species only tank but weren't really happy and all their fry were coming out still born and this was the only tank that they could of possibly been safe in that might of improved them and it's been wonderful for them! They're soooo much happier now and I've even spotted a fry that wasn't stillborn last night!) The least killifish are going to stay regardless because they're just a thousand times better for this change. But should I take out the 3 Platies so it's no longer overstocked even though they've been in better tank setups but this is the happiest I've ever seen them? And they also make all my other fish in the tank much much happier as well. Or should I just up my water changes either by volume or times per week? I mean i keep my levels at what I've been told was safe but I CAN keep them at even lower levels to make this safer. I'm not sure which is the best option because I know my stocking is incorrect (i knew before i added any of them) but I also know they're extremely happy with this setup. I'm torn between being correct and their happiness. There's also another tank that I had to move my cories into that was incorrect (put them in my betta rescue tank) the bettas are all rehomed now. But my cories went from the happiest I've ever seen them with these bettas to extremely depressed and spent 3 days refusing to move after the last of the bettas left. I knew the tank was incorrect. I fixed it. But my cories have suffered greatly due to depression. I just don't want to repeat that mistake. Because although I've added some new fish buddies for them after that 3rd day because I couldn't take them being this sad and they're not nearly as depressed anymore. They aren't anywhere close to as happy as they were with the betta rescues. But I know they shouldn't of ever been with a betta. Im at a loss. Again theres no actual issues with the tank other than I know they shouldn't be together. But is it more important to follow what you know is correct. Or what your fish do best with?