01-20-2012, 12:01 PM
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It's amazing how much water filtration is misunderstood. I'll refrain from harping on the silly 4-10 times water flow through the filter notion for a moment to focus on what happens to detritus in the filter...
Hobbyists buy into the notion they need all sorts of water flow to get that fish/plant waste into the filter. Powerful (sometimes multiple) filters and power heads...Out of sight, out of mind.
But what happens to that waste in the filter. All that waste and highly oxygenated water creates a buffet for decomposition bacteria to work overtime to break down that solid waste. With the high water flow, like compost tea, much of the slurry becomes suspended in solution and the dirty water gets pumped right back into the tank. Now if it's a heavily planted tank, the plants would use this (but then the plants would also use decomposed detritus in the upper layers of the substrate) otherwise, it's just dirty water that fish have to live in!
Enter the (weekly) water change - far more than just nitrate removal.
So, in conclusion, it is far better to let detritus (mulm) settle on the substrate where it will slowly, naturally decompose and optionally be removed with the weekly water change/gravel vacuum. Let the far less powerful filter just filter the water column without creating a torrent to collect every scrap of waste.
In a heavily planted tank, little if any external filtration is required - rather we just need gentle water flow for circulation (which is why we hear how well a modest sponge filter works in the planted tank).