since I've been back his respiratory infection's come back with a vengeance
He needs to go to be seen by a vet. That is really the only answer.
Apologies if it sounds harsh, but if he was showing signs in December, then odds are it has been there all along and is not going to get better without vet care and antibiotics. An RI, once it sets in, does not heal itself.
Taking into consideration his off-sided swimming, squeaking, etc. it is something to be very concerned with, and in my opinion is much higher in priority than shedding, UVB lights, water condition and eye problems.
With that said, putting him near a cold window is not a good idea. He needs warmth - 80 Fahrenheit at minimum.
Turning off the UVB is to give his eyes a break while the bulb goes through a burn period. He will be OK without a UVB light, but he cannot be put in / near cold.
Wispy shedding skin is typically due to either water that is too warm or poor water quality.