how many fish fit in 29tank?

[trinac]

Its up to you if you want one or not. In a mechanical filtration system it will catch the particles in the water, and you can also add in additional biofiltration media, and a lot of people put activated carbon in a mechanical filter. Activated carbon will keep your water clear as well as removing any odours and absorbs coral chemical defense.

You can go for a really inexpensive hang on the back too for these, or a canister. Canisters are more expensive and I feel like people kind of forget about them - hence the reputation of nitrate producers. They work very well so they have to be cleaned out regularly. I know some people put smashed up rock instead of the foam pads. I am not sure this is as effective for removing particulates, but its more biofiltration and less maintenance.