Sorry if this is a late reply!
The turtles will need 10 gallons of water PER inch length of turtle! If your turtle's shell (ex) is 6 inches from head to toe, a 60 gallon tank is the LEAST. I usually give my turtles some room, a 6 inch turtle I would give maybe 75-100 gallons. (That's just me)
For breeding them, I would get a larger tank, and somewhere in the tank( a nice corner) make a "nesting area" of small pebble and a darker place (like a cave!) for the female and eggs. An extra tank on the side for the hatchlings would be wonderful! And if you want to sell the babies, you legally (in America) have to wait for them to be 4 inches long to sell. You can gift them for free, but selling any 4" less terrapin is illegal. So make sure you have some room!
As for plants! Good water plants for turtles are:
Amazon swords
Anacharis
Duckweed
Frogbit
Hornwort
Nasturtium
Pondweed
Water fern
Water hycancinth
Water lettuce
Waterlilly
Water milfoil
Water star wort
These are a nice variety of non harmful plants!
Filtration: I wouldn't recommend using the typical fish filters, for turtles are quite messy! A big pet store or amazon even, carry nice perfect turtle filters, camouflaged as rocks, to help beautify the tank. The more turtles you have, the easier it is for them to get sick, so a good filter/cleanliness can stop salmonella!
Lighting: there are many different types of lights/lamps to get, depending on the size and shape of your tank. UVB lighting is SO IMPORTANT for turtles to grow correctly. UVA is also important, so 2 different lightbulbs may be needed. The basking area must be around 90 degrees! The avg water temperature must be 75-85 degrees for turtles to digest and be active healthily in a tank. The heater you can get at most petstores, or amazon (for cheaper) and are easy to find.
And I am glad he gets along with your fish! My little RES has 2 goldfish as best friends! But still eats the new fish I put in. >o<
I am going to test out a few bamboo shrimp/cleaner shrimp for my turtle tank. (She has issues catching prey) so I think as long as shrimp being a turtle snack, they can help clean the tank! Before they may be eaten!
The diet is very important for the turtle as well, cabbage and spinach are NOT to be fed to water turtles! (I'm sure you know!) but for breeding a healthy pair and for healthy offspring, a variety of protein and vitamin A and K is very important! Reptomin offers the best vitamins and treats/foods to give to your turtles.
I wish you and your turtle a happy time! ^o^
