Under Gravel Filter Is Gunky

  • #1
HI guys,
I have a 29 gallon tank with 2 fan tail goldfish in it (still little guys). I run an under gravel filter with an air pump and a fluval 300 GPH HOB filter. The tank is about a year old, water parameters are good, fish are healthy, etc. My question is: is it harmful that the under gravel filter is growing some sort of... gunk... under the plates? I can't see it (tank is on a dresser so I can't look up the bottom) so I don't know how bad it is but once every couple of weeks I do part of my water changes from the under gravel tubes and all sorts of junk comes out. It is either brown or white variety of junk. Should I be concerned? I just bought a bigger air pump for it hoping that that would help. Any ideas?
  • #2
That is common IMO with UG plates .
The smallest particles settle all the way through the gravel and such.
I would just try to suck it up though the tubes a little more when changing water .
IMO it is not a big problem unless left unchecked .
Sounds like you are doing fine ..
Vacuuming the gravel more may decrease the amount that makes it through also ..
  • #3
Yep, once upon a time, when UG filters were high tech I used them a lot. They always form that gunk underneath them, although mine was always brown; never saw white.

I had a brain storm that resulted in a HOB power filter drawing water from one end of the tank and discharging it into a space created between a plate siliconed across the other end of the tank. The plate extended from above the water surface down below the gravel to within a half-inch of the bottom glass. A homemade filter plate covered the entire bottom; the filtered water flowed under the vertical plate and into the space beneath the filter where it then percolated up through the gravel; i.e. a reverse flow UG filter. The whole idea was to reduce or eliminate the accumulation of gunk.

It gave me a nice convenient spot for hiding heaters, etc...and had no visible effect on gunk levels whatsoever.
  • #4
Without knowing the specifics of your setup it's hard to say for sure, but the size of the air pump is usually not the biggest problem with flow through a UGF. The bigger issue is the poor design of the uplift tubes. You either get a fairly open tube with large, poorly distributed bubbles, or you have an air stone that gives good bubble distribution but blocks the flow of water. The Czech air lift solves these issues by generating lots of small bubbles without an air stone being in the way. If you're moderately handy you can
, or you can buy a manufactured one from Swiss Tropicals. This won't really solve the problem of gunk building up underneath, but better water flow might get the bacteria to break it down before it settles on the bottom.
  • #5
I run conventional undergravel filters with powerheads. I vacuum half the tank each week.

I never have gunk under my plates, but bacterial floc accumulates in the gravel and is cleared when vacuuming and then grows again.

This is where the biological filtration happens so it is important to have the floc and not to remove all of it. It is also important not to let it build up until it blocks the water flow through the gravel.

Its easy to see how the accumulation of floc could be increased or decreased through feeding and cleaning.

I know my aquarium and what it needs to achieve this balance.

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