I have a fluval 304 external canister filter, and the flow rate is really very high for my little 37 gallon tank.

Does anyone know of any mods that can be done to lower the flow rate without causing a scary strong pull at the inlet? Wondering if the impeller could be altered/replaced or something like that. I could do with taking the flow down by half.

Hmmm... I thought this canister was one of the few that has adjustable flow rate?
Then again I could be wrong. I had one 4 - 5 years ago and there might be several generations of the filter. I think mine was called 304 MSF and it had this adjustable clamp (aquastop?)...

alas no, i wish it was though.

You can get a small "ball" valve to place in the filter output and use it to restrict the flow. Restricting the inlet flow is hard on the filter pump, but restricting the output won't hurt it. I had one of those Fluval 304 filters on the 120 gallon tank I had, and it was too little flow for that size, so I had the opposite problem.

I just change the direction of flow.
Just have the flow hit the back wall, add more holes to the spray bar, shoot most of the current into the wood/plant beds etc to reduce the flow. This can keep those dead areas under the wood good and clean. You can also direct some of the flow downward intio the gravel layer.

Play around with it, you should be fine with that filter on that tank size.

Regards,
Tom Barr

Interesting ideas, thanks guys.

Right now its just got the standard fluval outlet which pressurises it quite alot, ive actually thought maybe of splitting the flow with a T piece, I have quite a few dead spots around.. such is the way of annoying 4 foot, 12 inch wide tanks.

Do you think a spray bar might be better, maybe aligned from one end pointing to the other?

edit: just been looking at plumbing fittings, lots of sizes, my fluval hose is about 20mm(ish). Do you glue them into the fittings? (like the T peices etc)

You certainly should not reduce the flow in such a long tank.

Experiment around with differing flow patterns

Regards,
Tom Barr

Ive taken the fluted outlet off, and just have the pipe outflowing with nothing on it.. soooo much better, taken the edge off the initial boost, but left the volume of water moving around. So I think thats much much better it also seems to move the bigger bubbles from my mister about better as well.. so im happy bunny now

What about adding to the head length? Like inserting a piece of tubing, there'ld be some math involved though.

don't glue em , use zip ties of a pleasurable color...