If plants do the bio-filtering, why do some suggest 'overfiltering'?

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Junior Poster
Mar 22, 2008
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Planted tank newbie here, and I've been trying to learn, so here's another chance to help educate me! :D I've read that the plants in a heavily planted tank perform bio-filtration, getting rid of ammonia, nitrates, etc. In fact, nitrates need to be dosed in a high tech tank. So, if that's the case, why do I also read the 'overfiltering is much better' type comments? I'm setting up a 75 gallon, pressurized CO2, 3.5 to 4 wpg. I was going to use one XP3, but the more I read, the more I find advice that one XP3 won't be enough on a 75 gallon like the one I want to set up. That I should also set up a second filter. If I loaded two filters up with bio-media, wouldn't that take away nutrients from the plants? Or are they just for mechanical filtration? Why wouldn't one XP3 be enough?

I'm so confused...:p
 

tedr108

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The big thing you will read about here on this site is flow or circulation. Really good flow is encouraged so good nutrients get to all of the plants ... it is also healthy for fish, as they get more exercise. Plants do block circulation quite a bit, so in a heavily planted tank, you go for more flow than is recommended for a simple fish tank.
 

20 20

Junior Poster
Mar 22, 2008
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Thanks for the reply. What is the role in the filters employed in planted tanks, simply mechanical filtration and flow with the plants handling the bio-filtration? Or should the filters play some part in bio-filtration also? Still trying to get a handle on whether I need both the XP3 AND the XP2 on a 75 gallon heavily planted tank or not, and why.
 

richardsantink

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20 20;24113 said:
Thanks for the reply. What is the role in the filters employed in planted tanks, simply mechanical filtration and flow with the plants handling the bio-filtration? Or should the filters play some part in bio-filtration also? Still trying to get a handle on whether I need both the XP3 AND the XP2 on a 75 gallon heavily planted tank or not, and why.


In my situation, I have coldwater macro algae in my tank, and although I do more circulation than filtering, I do still skim, and remove particulate matter using an undersized canister filter (Eheim 2028). My canister has the wool in it, that's all.

As you no doubt know, detritus forms all over the place, and good circulation/filtration can help remove the floating bits...

RAS
 

tedr108

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Plants can use up only so much ammonia and nitrites. Yes, they are like bio-filters in a sense (and pretty good ones), but they are not so good as to render bio-filters useless. Since ammonia and nitrites are very toxic to fish and other critters, the bio-filter simply helps convert ammonia and nitrites to nitrates, which are much less toxic to fish.

The mechanical filtration is important too, of course.

I'm in about the same boat as you regarding the gph of my filter (260gph to 50G) compared to your XP3 and your tank size (350gph to 75G). I consider my filter underpowered (and want to upgrade to an XP3 actually). I make up for my current filter in 2 ways: 1) My CO2 is distributed via a 185gph powerhead, so I get a lot of extra flow during the day (you should see my plants swaying), and 2) I run a Marineland Emperor 280 gph bio-wheel filter all night long (on and off a few times per day to keep the wheel moist).

Honestly, I'd rather have a more powerful canister filter and remove the Emperor completely -- for aesthetics alone.