I just got a 55 gallon long fishtank for my two goldfish i got from my neighbors. They are super small, only a couple inches long, and i dont want a filter that will suck them in. I want to have a lot of plants and the fish are already 5 years old (according to my neighbors) and probably wont get bigger. I already have some black aquarium sand and might add a patch of gravel. I have experience with sponge filters, so should i go with those or do you guys recommend a different one based on experience? Also, what tankmates might you recommend for goldfish of their size?