I have one male fighter fish is a 4 gal tank, it has a filter and heater (yes, he's spoilt).

The problem is, he has extremely long fins and not much intelligence. He likes to hang around in the corner near the filter and heater to make a bubble nest. Some times he swims to close to the filter inlet and gets his tail sucked in the filter (not to far just enough so he can't swim free). He's been lucky I've been home to turn the power off so he can swim free.

The filter is a very small internal powerhead filter, what could I do? I wouldn't even know where to start with building some kind of cage around the filer. Anyway to get him to build a nest some where else?

You could buy a small fish net and cut off the netting to wrap around the intake. We did that in my old tank when we lost the original cap.

Props for taking proper care of your betta. The net sounds like a good idea, but if it doesn't work, i think it would be worth it to buy another filter. You can get mini filters for pretty cheap.

How did you attach it? Rubber bands would degrade yeah? I guess I could cover the whole thing hmm

net withrubber bands, twist tie or zipties, vacuum filters can be cut to size or sponge filters on intake tube. fluval has some for the intake on their canister filter it works on a aquaclear or similar sized intake tube. here is an example of a sponge filter over a whisper mini10 power filter. remember if flow starts to slow down, rinse them good and squeeeze them out good, you should figure out the little quirks depending on what you use and what filter its on. good luck

the more pourus or course the better. they dont plug up as easy or slow down the flow rate as much ... a brine shrimp net should work pretty good. here is a pic of the fluval canister intake prefilter.they are courser than a sponge filter... great for aquaclear or simular intake.