Cloudy Water

Hi I have an aquarium running for 2 months now 36x14x14 inches nitrites 0.
3 adult guppies 7 baby guppies 1 Queen Pleco 5 neon tetra 3 black tetras and
1000 snails. I change 10 litres water a week. I vacuumed the gravel a
month ago and a day later the water went greeny brown so bad I couldn't see
the fish. I had to clear it by using greenaway. The same thing has just
happened again after gravel vacuuming. Is it really necessary to clean the
gravel my tank is well planted. It is fine until I clean the tank. Also
could I keep a clown loach with the fish and size tank .

Hope you guys can help I am still learning.

Steve (UK)