I've had my new tank set up for about 5 months now and I've only lost one fish and I just want to make sure all my fish as of now are healthy. It's a 30g tank with a fluval50 filter and an elite800 air bubbler. I do all regular cartridge changes when needed along with adding chemicals. When I first set up my tank I cycled it for 2 weeks with fluval biological bacteria and I use nutrafin aqua plus waterconditoner as a weekly supplement and for water changes. I also put in fluval biological bacteria weekly to maintain a safe environment. I test my water weekly and it seems to be okay from what it says it should be for my fish. My ph is 7.4 with ideal alkalinity, soft hardness and nitrate is in the safe zone. My tank is lightly planted(plastic) with one cave and a few shells. I have 4 zebra danios, 9 platy fish and a golden algae eater in the tank right now. When I first set up my tank the only fish that I had was the 1 zebra danio and 4 platys. They were in a 15g tank before I bought the 30g. One platty was pregnant and gave birth to her fry and most were eaten except 1 which I managed to save and raised in a breeding tank. That's why I had 4 plattys(had 3 till the little baby came along). I sooner realized I needed to upgrade so I did so. I then went to my local pet store and resuced 3 more zebra danios(I know they're schooling fish but the one I had did no mind being on his own, just decided to get him some friends) and 4 blue moon plattys. So after buying my new fish I was up to 4 danios and 10 platys. After a couple months of being in the 30g together everything was going fine until one of my plattys passed of what I believe was clamped fins. It showed all the signs of this disease. Before this I still did everything I was suppose to do(water changes and medication). None of my other fish seem to have been effected by the disease. After he passed I did a big water change and all my fish still seem to be fine. When I first entered this hobby I basically went by what I read on the internet and what I was told because I had no experience keeping fish. I've somewhat built my own knowledge about my fish. So right now I have 4 danios and 9 plattys. They all seem to be at the best health but I just want to have some experienced opinions. I think some of my plattys may also be pregnant. and another question I have is regarding one of my danios. It is the oldest fish I have out of them all and it seems to be quite larger than the others and I'm just wondering if he's maybe a giant danio. Any suggestions are greatly appreciated and I thank you for hearing me out. I will attach photos of all my gorgeous fishes and the tank and the stuff I use.