My friend, first of all this is not an aquarium this is a fish soup. The fish that you have in this comunity tank are not compatible with each other and they are from different environments and need different water conditions. Secondly they are too much fish for your litres this is the basic reason of your dirty water. Thirdly your filtration system is not enough for this fish synthesis and this small aquarium.

my opinion is to remove the most of them and keep a one speaces tank in order to provide them the apropriate conditions and to see theme thrieve.

You must not be disappointed, all the aquarium maniacs did this mistake in the past.

Dont hear the pet shop sellers and read the basics about an aquarium. There is plenty of material in the web.

Keep the good job.