Yes... absolutely. I currently have a 55 gallon running enough filtration for about a 125 gallon tank (partly because the tank is overstocked). The water stays crystal clear and all the levels are great. I also have a 20 gallon running filtration for about a 45g (substrate is sand in there, less "room" for the beneficial bacteria so extra room in the filters and helps create water flow!). The only real difference is space it takes up and the amount of flow or water current. In the 20 gallon I have 2 hang over filters and a submerged filter.... it creates a decent current which my fish love and keeps any debris from settling on the sand, so as long as your fish don't mind the extra current (which they shouldn't for the 20g filter in a 10g, you still won't have much current really) then you're good, actually you're better than having a 10g filter system. As for the temp, just closely monitor the temp so you don't have your fish in really hot water. The extra wattage of the higher power heater could potentially get your water too hot, so just make sure you have it set to a good temp, which will most likely be a bit lower than its "neutral" setting.