1 more turtle?

Question
i have 1 large red eared slider i rescued from a family keeping him in a very small tank (pet store) and a small eastern painted I also rescued. From a snapping turtle as a hatching. He doesn't have one of his legs but he moves around fine.They are in a 155 gallon tank. Can I have 1 or 2 baby turtles possibly? (cooter or yellow belly) I saw that they get big though. (i don't know the humidity.) One rock for each turtle plus an extra (large) corner suction cupped rock. (sometimes they share.) They have 2 regular heat lamps and a night lamp.(its a custom tank so i cant find a proper cover) I believe they are from Zilla. I don't know the wattage, or the UBV. I don't know if the previous owners brought him to the vet. The large one sheds and the small one has never. I give feeder fish to them and 6 pellets to the big one and 3 to the small. In the morning and afternoon. I give 4 and 2 before I go to bed. I just fed them 30 minutes ago. I cleaned the tank on Friday. no other animals in the terrarium. I was wondering if i could possibly get more turtles. Thanks a lot for your time. PS. i have a small filter a heavy duty and another tetra fauna waterfall filter. the tank stays very clean. i am sorry if i'm waiting your time.

Answer
Hi Lily,

You're not wasting my time, but I don't think you're really considering what I'm trying to tell you.  The number one factors in keeping turtles healthy are:  plenty of room, water quality, temperatures and UVB, and diet.  So let's look at each factor one by one.

Tank size:  I'm not sure if you have them in a 40, 150, or 155 gallon tank.  40 is clearly too small for even the painted turtle.  155 is probably adequate for the turtles you have, but adding more turtles would really require a larger tank.  Sliders and cooters both get big, which of course means they need more room.

Water quality:  There's no possible way to keep the water quality high enough with the filters you have.   if the water looks clean, that doesn't mean it really is clean.  Turtles are dirty, and you need a powerful filter to maintain the water quality.  Based on the 150 gallon tank size, you need a filter that can handle 300 gallons.  If you add more turtles, you need to increase that capacity.  Nearly all the health questions I get about turtles are related to lack of water quality, either because of a too-small tank, poor filtration, or both.  If you feed in a separate tank, you can keep the water cleaner longer, but you still can't get away with using an inadequate filter.  

Temperatures:  You need adequate basking space for each turtle, with a temperature (on the basking surface) of about 88-90 degrees.  There should be enough room for both turtles to bask at the same time to adequately warm themselves and dry out.  If they can't bask properly, they can develop skin and shell problems--this also often happens if the water is too warm or the basking temperature too low.  You don't, however, need to provide night heat unless your house is very cold (low 50s).    

UVB:  Turtles need UVB in order to properly metabolize calcium; without it, they will develop shell and bone abnormalities.  This will be less obvious in adult turtles (but still significant), but hatchlings and juveniles will not grow properly, their shells won't harden, and they will eventually die.  In the wild, they obtain UVB from natural sunlight, but in captivity, they need a high-quality UVB-specific bulb to provide it.  Zilla bulbs are not good UVB bulbs, even though they claim to be (I have friends who test UVB bulbs with solar meters).  Currently the two bulbs that I recommend for UVB are either the ZooMed Powersun or the ZooMed Reptisun 10.0.  The Powersun provides heat and UVB in one, needs to be changed yearly, and costs $40-50.  The Reptisun is a UVB only tube bulb, needs to be changed every six months, and costs about $25-30.  I would recommend a Powersun over the Reptisun, and is what I use in my enclosures.

Diet:  Pellets are a good base diet, and feeder fish are also fine, but you should provide as much variety as possible.  The links I gave you earlier have some complete diet suggestions, but you can feed worms, bloodworms, shrimp, etc., and should also be offering some greens regularly (dandelion, turnip, kale, collards, duckweed, anacharis, and so forth--limit any kind of lettuce).  The more variety you can feed, the better for your turtles' health.

It's important to understand that turtles are very tough and will survive even under poor conditions.  However, my philosophy is that if we keep pets, we should do our best to keep them as optimally as possible.  I know that you would like more turtles, but my recommendations are always based on what is best for the pet, and not necessarily what the pet owner wants to hear.  So in your case, I would work on improving the tank you have (filtration and UVB) before you consider bringing in more turtles.