I have read in many fish books that you should have one inch of fish to every gallon in your tank. Goldfish can get really big. I have one that is 16 inches and plecos can get up to 20 inches or so. So you have to figure the adult size of your fish. Goldfish eat algae too. My goldfish doubles in size every year (I keep him in a 300 gallon water tank outside all year round with a heater in the winter.) Plecos are more active at night. Also pleco will eat those vacation food waffers. Plecos will also grow to the size of their enviroment too, but in a big tank like that they will get very big very quickly. You can feed them veggies like green beans too. As they get older they eat algae less and less and you will need to give them something else in their diet. You can strap lettuce or zucchini to a rock with a rubber band too. Good luck on your fish.