oh boy, well that stocking list is your problem, the tank is massivley overstocked and 9i'm sorry to say this) obviously not being well maintained (comments about uneaten food just being left to rot, addition of chemicals you don't need, no knowledge of basic water chemistry levels) so it's no wonder the water isn't clean.
However that being said, you are in the right place for some help and providing you're willing to take our advice we'll get this mess sorted out for you no problems.
First thing you need to do is learn your basic water chemistry, it's the cornerstone of fishkeeping and without even a basic understand youre not going to get anywhere. Take a look through this topic, it explains in laymens terms what the different levels are, how they affect the fish and what you need to do to get them right.
[URL="http
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Once you've read that you'll see why you need to go out and buy a test kit, then when you've got some water stats we can confirm exactly where the problems lie.
The second thing to look at is your stocking list, you should calculate stocking on roughly 1" of fish per US Gallon of water. This is based on the adult size of the fish, your tank is roughly 50 gallons, the fish you have are as follows
clown knifefish - 10"
black ghost knifefish - 18"
kissing pink - 12"
red tail black shark - 8"
clown loach x2 - 24"
cory x5 - 10"
bristlenose plec x3 - 18"
whiptail plec x3 - 6"
common plec - 24"
bumblebee malawi - 3"
yellow lab malawi x3 - 12"
yellow peacock - 4"
jack dempsey x2 - 12"
daemon eartheater x2 - 12"
green severum - 6"
gold severum - 6"
parrot cichlid x2 - 20"
rusty malawi - 4"
upside down cat - 6"
so that's around 215" of fish, you should have around 50"........ there's no arguing that your tank is massivley overstocked. several of the fish get too big for your tank and are also not compatible with each other. You seem to like cichlids, but you need to chooose african or american cichlids (you have both and they shouldn't be kept together). If you let us know which fish you really want to keep we'll then try and work out a suitable stocking list based around those fish so you can then re-home the rest of them.
here's a guide to weekly tank maintenance as well, i'd advise you set aside some time to follow the instructions and give the tank a good clean asap
[URL="http
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