The Tank Is Getting Older...

[Bud]

We've had a 55 gallon freshwater tank set up for about eight years. The biggest mistake we'd made at the beginning was setting up an under-gravel filter. While it's been running all along, we quickly wised up and installed an external box filter.

Over the years, the tank's housed a tropical community, mostly tetras. For the last year, it's been the home of cardinals and glow-lights. The tank is filled with dozens of live plants.


The question is: can we simply pull up the vertical/uplift tubes of the under gravel filter, cover the openings in the gravel (where the tubes had been), and then declare the under-gravel filter officially closed? (Maybe "condemned" would be the better word.)

I'm afraid that if we do that, the water under the plates will cease circulating and will become quite nasty.

Thanks very much.

 

[KittyKat]

I felt the same way as you, when I decided to try an undergravel filter a few years ago for the fun of it just because I had a spare tank that had some with one.

If the undergravel is still running, it is likely to contain a considerable proportion of bacteria, so I recommend that instead of switching it off immediately, you gradually reduce the airflow (and thus the water flow) going through it over the next two months, and the external filter can then take over altogether. This can be done with the dial on the pump, if you have it, by removing one of the two airstones (if you have two or more tubes for the filter) or by slowly raising the airstones in the tubes (for example, by 1/8th every week).

Once this is done, you can just pull the tubes up and cover the holes. You are right that when the plates are taken up, things are not going to look pretty, but the water in itself is unlikely to become nasty and this is likely already the case anyway.

Alternatively, why not put the outlet from the external filter into one of the tubes (and block up the rest) to create a reverse UG filter? This actually works pretty well and reduces the need to clean the gravel, as the dirt is constantly pushed up anyway.

If it were my tank and I wanted the UG filter properly out, then I'd pull it up and swap to a mix of play sand and sharp sand while I was at it.

 

[OldMan47]

Welcome to the forum Bud.
You are right, the water under the filter plate will be quite nasty and will definitely go anaerobic. Unless you are ready to reverse your filter as KittyKat suggested, I would remove the filter plate completely. Just remove a bucket full of water and your fish, then remove the filter plate and get the tank running again. Top off the water and put the fish back in. It could take all day to do it right but it would remove any concern about the filter plate being left behind in an anaerobic state.