You are looking at filters for the size tank. With turtles you can't do that ! For a turtle alone in a 75 gallon tank being how messy they are you need a flow rate of 225 gallons with a turtle your size . Those filters are rated to low or you will be back where you are today. Plus you have the large comets in there too which are dirty fish ! Filters are rated for fish not turtles and come with media for fish not turtles you will need to modify media to fit a turtle. See :
viewtopic.php?f=9&t=30145With a filter under rated you will be cleaning every 4-7 days with large water changes ! It will be next to impossible to matain a cycled tank.
A baby turtle needs 2 x's the flow of fish , juviniles need 3-4x's flow and adults need 4-5 x's flow if you want to be able to control your waters parameters. Then you have a female which can get 12" needing the numbers on the larger side for a filter. Males only get 9". You do not have a baby turtle it's a juvenile in size.
Keep looking for filters sold in your area for a higher flow rate needed with turtles. Then again you also have the large comets in there too ? Even more filter is needed ! Or separate the comets into another tank and get Rosy Red minnows in with your turtle they are a much cleaner fish.
You need to be looking at filters like the FX4 if you want a clean / healthy tank. Also it has 3.7 gallons of media not a few oz's of media as some filters. A filter on that line with proper water changes you would only have to clean it every 3-4 weeks and you know how we all just love doing filter maintenance. This type filter would allow your tank to cycle better helping you with keeping it clean longer. Something on that line with a high flow rate and good media volume for all you have in that 75 now.
I do not own an FX4 I have a FX6 but the functionality is the same ! See my videos and how my water looks on 125 gallons water for Piggley 5" male RES. Here's a very short Xmas video so you can see.
https://youtu.be/HJ0BMahk_uAA filter sized to a turtle with proper media volume goes a long way.
Depending on what part of the world you live in and if you use a "price tracker" it can be in same price range.