I've recently bought red eared sliders(one week ago) and I'm not sure what to do because one of them appears to have shell rot(not too sure) and the other one has a pink tint underbelly. I got these turtles from Kijiji. The smaller one 5inches in shell length and the other one is 7.5inches in shell length. They both currently live in a 75g tank together, has uvb and heating bulb(from zoomed) , egg create lighting diffuser DIY dock, use a fluval filter, tetra 200w water heater(water is 25 degrees) and have been eating carrots and Wardley reptile sticks(old owner told me the diet) I'm not too sure what to do and was wanting some help. Also the tank start to smell pretty bad after the second day.
Previous owner offered a poor diet and poor habitat. To be blunt that75g even full is small for a total of 12.5" of turtles with an "ATBA". One is male for sure , other unknown , if both are males you will have to separate. Better photo of second one would help. If not today separation will come soon and a must.
Turtles those sizes should be on a 70% veggie diet !
UVA (heat) and UVB bulbs have a placement distance for them to do the job , most are at different heights that why a good amount of long time turtle keepers use two fixtures to achieve that.
Smelly tank , you need to spend more time on a proper setup. Will never be able to control that small amount of water for two big turtles. That's blunt but it's all about your turtles health ! A turtle need for every 1" of shell 10 gallons of water alone ! You have 12.5 " of turtle that's a 125 gallon tank of water alone needed. And if both males separation should come before one gets hurt or makes the other sick too. Either way separate.
Can you post a close-up pic of the area you think is shell rot?