To filter or not to filter...

[kreblak]

I have been reading a lot of contradictory information about filter usage lately. Some folks are saying that running a mechanical filter will cause nitrates to increase. I was told by my LFS that running a machanical filter with activated carbon is extremely necessary, and will decrease my nitrates.

Who is correct, and why would a filter cause my nitrate levels to increase?

[OrionGirl]

The general explanation for filters (and CC, UGF) increasing nitrates is that they trap the detritus in a location where the 'critters' can't get to it. For example, leftover food gets swept away into the filter, where it sits slowly decomposing. The ammonia/nitrites are broken down quickly by your bacteria bed. The nitrates are slower to be addressed because the location of the bacteria--somewhere deep in the low oxygen zones of sand and rock. If the food scrap is left in the main tank, a crab will grab it, or a snail, or a star fish, or worm, etc. So, before it can break down on it's way to nitrates, it serves as a meal for someone, and the resulting waste is less, because part of the original chunk stays behind and makes more crab/snail/starfish/worm.

So, if you clean your filter out regularly, it won't cause a huge increase in nitrates. If you start slacking, it will. CC and UGF have other issues as well, since they reduce the potential housing for the low oxygen bacteria and it's hard to really clean CC without killing off a lot of in bed fauna.

[kreblak]

I see, so if I'm understanding you correctly, filtering MAY increase nitrates by trapping decomposing organic matter in a location where the bacteria required to break it down cannot grow.

So, what would constitute regular cleaning of the filter. My filter uses replaceable activated carbon, which typically get used up in about 30 days. If I am replacing the carbon every 30 days, am I keeping the filter sufficiently cleaned, or does that allow too much time for detritus buildup?

Should I stop filtering with activated carbon alltogether, and just run the skimmer every few days or so? Also, is there a test you can get to check nitrate levels? I suspect that mine are high.

[VoodooChild]

Usually the maximum carbon lasts is a month. In a marine tank with all of the trace elements and other wastes it may last a few days, so basically after a week at the most it just becomes a bacterial bed. I wouldn't bother with carbon and just run it empty and use it for water movement. And unless your tank is a reef I'd just keep the skimmer going all of the time. That basically will do what the carbon does but obviously doesn't need monthly changes (though it really helps out if you clean the thing once a month).

[OrionGirl]

Yeah, basically. The mechanical filter doesn't prevent the nitrates from getting to the bacteria, rather, it allows the detritus to turn into nitrates sooner and in higher concentration.

Carbon will also pull out some other things you want in--more so than the skimmer. I would say that weekly cleaning would be the only way to prevent a mechanical filter from increasing your nitrates.

There are SW nitrate kits--I am constantly baffled by their absence from standard test kits. If you have corals, you'll notice they don't open up as much or as often when nitrates are high. Also, many fish will begin to suffer--poor color, poor behavior, ect. Keep in mind that nitrates are generally used to gauge the level of other things we can't test as easily, many which will cause serious problems. SW has higher dissolved solids than FW anyway, but it can still get too high. Trace elements, alkalinity, calcium, iodine, all of these things get depleted eventually--more so with either carbon or a skimmer--and water changes are the best way to dilute the pollution and provide the refill for the other things.

[makai]

i was leary at first also......

my filters have been used as a "glorified powerheads" for the last 5-6 months with no problems. I do a small 5 g water change every sat... just as a precaution. Some weeks the water doesn't even need to be changed. I wouldn't have tryed this without a skimmer though


my experiance;)

[OrionGirl]

Using a power filter without any media is fine, but not the same creature as using a filter with the OEM media.

[VoodooChild]

It can come in handy though. I keep crushed aragonite in might to buffer it. It could also be used as a spot for carbon if it were needed or a mini-refugium if you turned the flow down.