Red Ear Slider eye problem

Question
Hi, I have 2 red ear slider turtles. I have had them for about 4-5 years. They were in a 50 gallon tank that they were outgrowing and I realized it did not have the proper lighting. The tank had a glass top, so the UV light was being filtered. I just bought a new 120 gallon tank and moved the turtles. They were doing just fine in the old tank, but seem to be having a problem in the new tank. Their eyes seem a bit swollen and they keep them closed most of the time. They are eating and seem ok otherwise, but I had never noticed this is the old tank. I thought maybe something was wrong with the water and took it to a store to be tested. They said the water was fine, but gave me some water conditioner to put in the tank just in case. It seems weird that this problem happened when I put them in the new tank. I thought maybe it would go away, but it has been about a week and a half and nothing has changed. The new tank now has the proper lighting without anything on the top of the tank. Is it possible that it could be because they weren't getting the proper light for so long and now it seems really bright to them? I also had read that a water temp change could cause this. I don't know what temp the old tank was, but the new tank was set to 80. I changed it down to 78 yesterday. I dont see how their eyes could have gotten infected in a week from a new tank with clean water. I suppose it is possible, but I am not sure what to do. I put them in the new tank to make things better for them and it seems I have made it worse. Do you have any ideas or suggestions?  Thank you

Answer
Big changes, good or bad, stress turtles and an eye infection is a common result.

New tanks can have bacterial blooms, radically different chemicals, etc. More space is a big change, as is the light.

What I would do is:

1. Double check diet and make sure they are getting a balanced meal and vitamins. Vitamin A is often short when you see eye infections.

2. 78F is good normally, but if the turtles are ill, boost to about 80-85F.

3. Try either a Turtle Sulfa Dip or fish Stress-Coat medicine per directions. This should hel fight secondary issues.

It might well be a response just to the lighting. As long as they have access to shady and cooler areas, I would not worry tto much.