Hi getting my first 200l tank and wanted a powerful filter but where I want to fit the tank only have space for a filter that’s maximum 33cm high, is there any that are more compact or would one work on it’s side?
There is a loty of misinformation, or misunderstanding, in the hobby when it comes to filters. Filtration should be geared to the fish you intend. Too much current can stress out fish that come from quieter waters, while fish from ragin rivers obviously need more water current. When it comes to filtration, larger filters, faster filters, or more filters do not improve filtration at all, so there is no benefit. All you need is a filter that can handle the tank biologically.
A 200 liter (50-ish gallons) could have a dual sponge filter for a tank of quieter fish, or an HOB, or a small internal like the Aqueon QuietFlow. Knowing the intended fish, and if live plants will be included, will help pin this down more.
Every fish has it's own bio-footprint. Ember tetra is very small, they don't produce a lot of waste compared to a goldfish which is much larger and produces much more waste. Like Byron said it really is up to what type of fish and how many. Live plants also make a positive difference.