weakening HOB filters

My HoB filters on 2 of my 3 tanks have been growing weaker with weaker water flow. Anyone have any advice on dealing with them? also how often (if at all) does filter medium need replacing in them.

I've got a couple of hang on the back filters: a penguin 300 on a 38 gallon and an emperor 400 on a 75 gallon. Both seem to be fairly good filters, however if I let the water level drop more than a couple inches the emperor slows to a trickle. The penguin, on the other hand, seems to be quite the powerhouse. I was lazy about topping off the 38 last summer and let it drop about 7 or 8 inches low and didn't notice any reduction in flow. Created quite a noisy waterfall effect though.
I also noticed with the emperor, that refilling the tank doesn't always restore the flow. In these instances I have to take the filter off of the tank, disassemble it and clean all the gunk out of the area where the impeller sits.
I generally don't replace my filter medium, just clean it once in a while.

Generally all that's required is running water through the intake tube, which easily snaps on and off. You'll be surprised at how much crap you find in there.

Cleaning the intake tube and screen help a lot. You should also check the impeller and make sure it is clean and clear of obstructions.

Mulm in the filter medium can also reduce flow or cause bypass. You shouldn't have to replace the filter medium until it is just disintegrating, but it is a good idea to clean it every month or so. Just take it out and swish it in a pail of tank water, and use your hands to wring some of the excess gunk out. This opens the filter medium pores back up and increases the surface area available to beneficial bacteria as well as improving flow.

You can slow mulm buildup by using a prefilter- a filter sponge around the intake will work wonders.

Cleaning the intake tube and screen help a lot. You should also check the impeller and make sure it is clean and clear of obstructions.

Mulm in the filter medium can also reduce flow or cause bypass. You shouldn't have to replace the filter medium until it is just disintegrating, but it is a good idea to clean it every month or so. Just take it out and swish it in a pail of tank water, and use your hands to wring some of the excess gunk out. This opens the filter medium pores back up and increases the surface area available to beneficial bacteria as well as improving flow.

You can slow mulm buildup by using a prefilter- a filter sponge around the intake will work wonders.

Sometimes the problem is because the nylon or teflon impeller bearing becomes worn which can either reduce the rpm's or stop the impeller spinning. Sometimes a new impeller will solve the problem but some HOB designs do not lend themselves well to easy bearing replacement.

Edited by apistomaster, 17 January 2010 - 05:44 PM.