Water turning cloudy and some other things.

Ulyaoth

Since I went on vacation a few weeks ago I've been having some issues with my tank. My cousin was supposed to take care of it but he overfed the tank and caused a big algae bloom and even with underfeeding a bit and doing a few more waterchanges than normal(normally 50% once a week, done a few 20% in the middle of that) my nitrates are still high and won't seem to go down(hovering around 40ppm no matter when I test, whether before I change the water or like a day after, haven't tested my tap water yet I guess I should) and my platies have been acting really weird, other than when I feed them when they go into their normal feeding frenzy they've mostly just been hovering around the top of the tank hiding next to the heater and filter, or hiding in the bottom. Normally they'd be swimming all over chasing each other and nibbling at algae and the plants.

Also, water's getting a bit cloudy, like whitish, with a weird film building up on the glass. I have an Aqueon filter with one of those carbon filled pouches in the filter, wondering if changing it would help, but would that mean I'd have to watch the tank recycle or is the bacteria in other things in the filter? I never changed it, it says it should be changed every month but I thought that'd mess up with the bacteria so it's been since I started the tank in early January just the one filter cartridge.

redchigh

Most filters have a 'biological' media and a 'chemical' media.
The chemical media is the carbon bag, but there should be some foam, ceramic pieces, or something to work as biological.

You can replcace the chemical and rinse out the biological in TANK water without harming your biological filtration...

Whether it will help or not... I don't know.

Have you tested ammonia and nitrites?

Do you vacuum the gravel? I normally never do it, but in your situation, it might be a good idea...

Ulyaoth

Ammonia and nitrites are zero, just kinda high nitrates. Forget to say the rest, It's 16gallons, temp 78* 5 zebra danios, 3 platies, 2 goby plecos, a bunch of java ferns and an Anubias nana. I haven't vacuumed the gravel but since it's gotten kind messy lately I stirred it up with a net before I did a water change. Also rinsed out the cartridge already last waterchange in the bucket of old water, the water turned completely brown, but it didn't seem to help anything.

Also, about the platies, my water is kinda soft, although I've raised the ph to just above neutral with baking soda, the hardness is still only about 100ppm, I was wondering if maybe that might be bugging the platies finally, I know they're supposed to like harder basic water.

Ulyaoth

bump, same issue still.