water quality

Question
I have a red-eared slider (a baby boy), with a shell diameter about 6 in. in length and 4 1/2 in. in width.  He currently lives in a w=12 in., h=17 in., l=24 in. tank which I believe is 20 or 25 gallons.  I fill the water up to 12 in. deep leaving 5 in. of head room.  Overhead is the appropriate UV light for reptiles (specifically turtles).   use med. and lg. size river stones for him to dig in and ave an artificial piece of wood on the bottom and a floating platform.  The filtration is a Rena xP canister filter for  45 gallon tank that I purchased about 2-3 months ago, this is when the problem began.  

The problem is that the water develops a milky appearance in only a week, which has not been a problem for the past three years that I have had him.  There are sponges, sacks of carbon and zeolite crystals, and bio-stars.  When I put the new water in I balance it to pH 7.0, get rid of chlorine, etc.  I also use an all natural, bacterial pond clarifier by PondCare called Ecofix that is suppose to keep water clean and clear, as well as break down dead algae and increase oxygen, and Stress Zyme for a biological filtration booster (which I bought after the Ecofix was not helping much).  

I am currently thinking of buying something that releases air bubbles hoping that the milky cloudiness in the water is trapped gases that could be more easily released with the aid of the air bubbles (plus, it looks better aesthetically).

Is that going to help the water, or should I do something else (take into account that I am a college student and currently cannot buy new and bigger tank and/or filter)?

Answer
If your male Red-ear is 6" long, it is no longer a baby (about 1") and is at least a young adult (average adult size is 9").

The tank sounds great except for the overall size. The rule of thumb is about 10 gallons of water per inch of turtle, so yours needs a 60 gallon pool, or a 100 gallon tank filled about 3/4 full.

It sounds like you are doing the right stuff as far as most filtration goes (although the rated volume for the filter is about 1/3rd what it should be for a 6" turtle). My thoughts are:
- the biological colonies have not yet established. That takes 4-6 weeks to happen, and they are what processes a lot of the junk in the water.
- you may be over-treating the water. Most of us do perfectly well with tap water and a good filter. Chlorine and pH is not usually an issue unless yours is REALLY bad, but the rule of thumb is if you can drink it, most turtles can live in it. (Of course, if you are using a bacterial cleaner, you need to kill the chlorine- but again, you may just be putting too much stuff in the water!)

Have you actually checked the water for chlorine, ammonia, nitrates, etc. so you know what you are trying to fight?

Personally, I would (assumng the turtle is about 6" long, shell only, measured in a straight line (not on the curve)- what is called Straight Carapace Length  or SCL:
- Bigger tank. Most of us use a kiddie pool or big plastic tub at this size because of the cost issue.
- More filtration. Add a few cheapo old-fashioned 'corner in-tank' or similar filters if that is what it takes.
- Experiment with not over-processing the water. Keep a jug of water sitting out to de-chlorinate naturally but otherwise just filter it. Try this for a few weeks and see what happens.
- Get a couple water test kits and see what your real issues might be.