Filtration discussion

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Aquarium Advice Apprentice
Nov 12, 2003
Lisbon - Portugal
Hi guys!

My (salt water) aquarium has 200 litres (around 45 Gal) and I have a biological filter open to the water and a mechanical one connected to the bottom board.

The shop owner that sold it to me and helped me assemble it says that he has good results with the bottom filtration and that it keeps the aquarium cleaner.

The thing is that two other shop owners told me that bottom filtration is not good because a lot of the waste stays in the sand (I have thick coral sand) and gets decomposed there, polluting the aquarium.

Does anyone use bottom filtration?

I'd like to hear some more opinions on this.

That is what we call undergravel filtration or a UGF. I don't think anyone on here would recommend that type filtration for a SW tank. It will cause all kinds of trash to get trapped in your sand where it will decompose and turn into nitrates. Nitrates will cause algae blooms. Probably the most common type of filtration used in SW tanks here is the Berlin method. If you'll look on the left side of the home page on this site, you'll see an "articles" link. In there are several articles about SW tanks that you might want to read including one that explains the Berlin method of filtration.
The filterplate will also get clogged with sand over time making it less effective and eventually make it totally ineffective.

IMO you would be best to remove the filter plate and use the DSB as your filter. How deep is your coral sand? Is the sand grain very fine in size or is it more like crushed coral/shells?
OK, no more undergravel filtration for me!

The coral sand grain is large (more like crushed coral/shells) and the layer is around 5 cm (2 inch) thick. Excuse the ignorance (i'm only into salt water for about 2 months), but how do I use the DSB as a filter?

So, to use the Berlin method, I should add more live rock and gradually remove the mechanical filter media (I already have the skimmer)? Won't I then have the anemonae waste and such, floating around?

Thanks for the quick replies!
Loganj is right on track. Undergravel filters = bad, very BAD for SW tanks.

Actually, I'd leave the UGF plate where it's at and simply pull the powerheads and uplift pipes.
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