there's a bit of setup required but wasn't too hard. i did a full water change with putting in the new filter and now it's a little cloudy and junky. i was worried, but i was told this was a "biological bloom" of new good bacteria developing and it should clear up in a few days and then help with breaking down the junk. going to give it some time before i discount it.
i did a little more digging about the breathing, and actually found this in a post on another turtle forum site. it is a big reassurance!
It's perfectly normal to be able to hear a larger(4"+) turtle's breathing if you pay enough attention. It's one of those things you may hear unintentionally for the first time in 5 years, and then you'll hear it every time afterwards because your actually listening for it. Same with the hissing, he's just expelling air to make room for his extremities.
When a turtle is swimming around and comes up for air, it's heart rate is up from the activity and it breathes heavier, that is why you can't hear it while he's just chillun' under the basking light.
While those can be taken as symptoms of an RI, they must be taken in context with the general wellness of your turtle. You...as his owner will know when something just isn't right with him. If he's acting and eating normal, he's probably doing fine.
Besides, you ever really look at a turtles nostrils? You would whistle too if you had to breathe through those tiny things!

D
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