You might consider using your 10 gallon tank as a filtration sump set up with a 200 to 500 gallon per hour submersible pump which pumps water from the 10 gallon sump via 1/2" PVC
pipe up into your 55 gallon tank. By using a 1 1/4" PVC
DIY overflow for the return from your 55 gallon fish tank back to the sump you'll have outstanding water circulation and filtration with quiet operation. I keep only goldfish and Koi and with this set up including under-gravel filtration, a wet-dry drip or trickle filter in a 10 gallon sump with a 500 gallon per hour submersible pump as well as a large aqua-tec external filter, my tanks are doing very well. My fish are healthy and plump and the water in my tanks is clean, sweet smelling and clear. I do religious 10 gallon water changes every 7 days and add aquarium salt in the amount of one and a half rounded teaspoons to every 5 gallons of water. It helps with the general overall health of the fish and tank and I highly recommend it for Koi and goldfish. I never allow direct sunlight to fall on the tanks. I vacuum the gravel at the bottom of the tank and remove 10 gallons of this dirty water into two 5 gallon jugs. I keep two 5 gallon jugs of fresh treated water with aquarium salt added on hand to refill the tank after clean-up. This way there is no issue in possibly upsetting the bio-balance of the wet-dry drip filter. In past I've only had problems when I neglected to follow the rules of cleanliness. I never feed live food and I always feed three times a day with a variety of flake and pellets. The use of a sump tank for biological filtration, water circulation, temperature control and airation is probably the best idea for stopping most of the problems with fish tanks. Even so, I've found that water changes on a regular basis are key to problem free fish keeping. I also check the PH in my tanks every week keeping my eye on nitrate levels at the same time. I use multi-purpose test strips for this and they let me know exactly what's up with water chemistry so I can adjust it as needed. I also use a large air stone in all of my tanks and also insure that I have strong air flow to the small air stones in the under-gravel filter system. There is also a large air stone in the sump. To achieve this I use two dual air pumps for a total of four feed lines per 55 gallon tank including the sump. One line goes to the sump, one the the large stone in the tank and two lines split to feed the four stones in the undergravel filter. I have three inches of gravel at the back of the tank tapering down to one inch at the front of the tank. Again, I vacuum all of this gravel every 7 days when I do the water changes. See my Post entitled "Greetings from Roseville, CA
" to read more about my set-up. I only keep goldfish and Koi because I love them. I take pride in my fish and try to always improve the art of fish-keeping by implementing the latest ideas.
Best and warmest of regards, Frank / fj109