So far, so good with my big fat gold fish (pictures posted above, of 5-7 inch goldfish). I don't have a real filter in either tank.
With hardy fish (like carp, green sunfish, river chubs, etc.,) I've had very good success without actual filters and pumps. I've been doing this for years.
Since early October I have had two 10 gallon tanks running, each with two big goldfish -- that's a whole 'nother story! (Grandkids and aquaponics.)
In using this method a number of times over the years with "trash fish". I've never bothered to take any measurements, so I have no idea of ammonia levels, pH, D.O., etc. These are fish that just have sentimental value to grandparents, grandkids, etc., or they are my baitfish. If they perish, they perish!
So, please don't take this as the way to grow and keep fish alive. But, it is a simple and inexpensive method of keeping rough fish.
I buy pea gravel, and other road gravel, rip-rap, etc., in 10-20 ton quantities at a time. So I always have gravel available. All I do is go out to the pile of river pea gravel near the barn, and grab a bucketful that goes into the bottom of an aquarium about 1 inch deep.
For the 10 gallon tanks I have some inexpensive Wally-World air-stones that stretch nearly edge-to-edge lengthwise in the aquariums. They are placed at the very bottom of the tanks where they are nearly covered with gravel. For these tanks I have a dual output $10-$15 dollar air pump rated for a 50 gallon tank.
I feed the fish twice a day. I use a "siphon vacuum cleaner" made for aquariums to clean the gravel about once a week. These cost about $5-10 in any aquarium type fish supply department. If I see algae on the insides of the aquariums I wipe it off with a paper towel before refilling the tanks. The cleaning takes about about 1/3 of the aquarium water. The water taken from the pea gravel can actually be pretty nasty. Because I don't have any heaters in the tanks, I'm able to just refill the tanks with well water. The water that comes out of my taps is usually within a few degrees of the aquarium water that is here in the basement.
Enough. I still plan to go get some larger tanks next week.
