Well my frogs have a filter powerful enough for a 200L tank in their 34L tank, water two thirds full and they are as happy as larry, so yes you can use a filter, try to keep the current to a minimum as they are not great swimmers, mine is turned to face the back of the tank, they will be good, I found without a filter, the ammonia rose quickly even with only 4 frogs in a 10g tank.