Tropical Fish Keeping - Aquarium fish care and resources

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twocents 10-14-2011 04:35 PM

Shutting off air foam filters
Byron, in his missive on plant care, made a point that oxygenation is not needed, and may be even somewhat detrimental, in a heavily planted tank.

i have in tank cube foam filters run by a single air pump, in all 5 tanks. Since they are always bubbling, I was wondering if a good compromise (to allow some CO2 build up for the plants) would be to put the pump on a timer and shut it down overnight to give the co2 a chance to build up.

Any thoughts?
Byron, any thoughts on this?

DKRST 10-14-2011 04:49 PM

The desirability of water movement (oxygenation) depends greatly on your fish, and to some degree, your plant stocking levels. If I don't agitate my very heavily planted 55 gallon tank's surface, my fish have faster respiration rates (gill movements) and my corys make more frequent "trips" to the waters surface for supplemental O2. Biologically, plants actually consume CO2 in darkness and this, in combination with your fish, can raise tank CO2 to harmful levels overnight in a heavily planted tank. Plants only generate oxygen when they can photosynthesize (under light). If anything, I would recommend agitating the tank water when the lights are off. That will benefit both the fish and plants.

That being said, minimal surface movement is good in a planted tank to minimize CO2 loss.

twocents 10-14-2011 04:57 PM

Thanks. I have control valves on all the lines so I can control the amount of air running through the foam cubes. In the large tank, the movement at the surface is not much, but in the smaller tanks, there is agitation.

Also, don't you mean plants produce CO2 during the night...?

I have a thread elsewhere: the foam filters are the only filtration. In a way, I am even wondering if they are necessary. However, since they are air driven, they do provide oxygenation.

DKRST 10-14-2011 05:54 PM

OOPS, my mistake, you are correct, I meant plants consume O2 and produce CO2 in the darkness. Sorry about that!

zof 10-14-2011 06:47 PM

Just from a water movement stand point I would keep the air going if the sponge filter is the only source of water movement, unless your injecting co2 theres not that big of a downside to using air on a sponge filter in my opinion anyways. Positives outweigh the negatives unless you are going hi tech.

Byron 10-15-2011 11:37 AM

A filter should never be turned off but kept running constantly. Note, I said filter; meaning the tank's "filter" apparatus.

As for oxygen, it should never be so low that fish shows signs of it. That signifies overstocking. Even in heavily planted tanks this should never occur unless there are simply too many fish in the tank. I have never had issues in my planted tanks, and they have a lot of fish.

When CO2 is added during daylight via diffusion, it should be turned off at night. This can cause trouble, as CO2 being pumped into the tank at night is only going to build up. But in natural or low-tech systems, it should not be an issue.


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