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.
Only a week with you but you must offer a better habitat than that previous owner. Read all stickies at each topic for help on this forum. You have a lot of catching up to do to get these two healthy again. Another good read is :
http://www.redearslider.com/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 copy / paste / answer these questions in some detail ( type , size , wattage , filter model ... not just yes or no :
viewtopic.php?t=2142 Also a good read :
http://www.wetwebmedia.com/fwsubwebinde ... arrelB.htm
Posted: Fri Jun 16, 2017 10:01 am New turtle owner and I need help