Please read all , this is from exo-terra not just me. May be the MV you got or not but they have great info. Use there star chart select your animal then go to there bulb charts and choose what fits the requirements. They made getting the correct bulb very simple with their Star Rating chart . A great help to beginners. Myself I am a Mega Ray user but that's just my choice. The exo-terra star chart is very accurate with all species listed.
Only numbers in that area “265” for for a 12” placement is on exo-terra #PT2193 which is a 160 watt mv. You state a 125 watts and there chart (see below) says “165” on a placement of 12"s. Do you have the 165 watt mv or 125 watt , your statement was 125 watt ?
You are “only” looking at one of there charts but one must use “both” charts to match the pet to the proper wattage size and placement . There chart is for the best health of your pet , not just my statement/advice , please look at both charts for wattage and mainly distance placement . I like to see this turtle in your family for decades.
You are deciding from one chart only. They offer a index scale chart for different animals ( see “there” index chart below) to help people understand what’s needed on “MV’s” with specific species. A RES turtle is "2 stars" on needs not at 5 stars like for dragons and lizards for that reading you stated (265 at 12" with a 160 watt on there chart). They offer that to help one get the right bulb and mainly the correct "placement" for a healthy uW/cm² reading for your species !
http://www.exo-terra.com/en/products/solar_glo.phphttp://www.exo-terra.com/en/explore/uv_rating_index.phpAll I trying to do is help people understand what’s best for the turtles. Just like there chart's , what’s best for the turtle .
Using both charts will help you see what’s needed . In my decades most popular range is 20-100 uW/cm² and some go up to 150 range for aquatic turtle.
Hope both charts offer better understanding , than how I'm trying to say it. You may want to read up on what happens when too much UVB is given even with RES turtles having two sets of eye lids. Blindness is just one problem...many other issues too. Too many beginners think more is better but "not true" and the turtle pays the price !