BLUE TONGUE SKINKS

Looking for some advice...I have owned my BTS Charlie for over a year now, from 1 month old, and he has been a joy to have. He loves to dig and bury himself in the substrate, making tunnels all through his tank.
For the last 2 weeks Charlie hasn't come out to eat (he has skipped a feed every so often, and went on a food strike last winter for a bit so I wasn't too concerned), then this Thursday he finally did come out, but I noticed his third eyelids were swollen, with the right eye being almost fully covered by the swelling. He would bulge out his eye and try to rub it against things, so I took a few pictures and videos, which I later shared with the vet. I immediately called the vet, but wasn't able to take him in until Friday afternoon. After making the appointment I flushed his eyes out with saline, and a few hours later the swelling had gone down, by morning they looked normal. The vet said he was in great condition, no signs of infection, cataracts or anything else, and that it was likely cause by irritation, that they had found a hair (likely from the coco husk substrate) in the worst eye. He said I had done the right thing, and to just flush the eye if it happened again. His feeding day was Friday, but he refused after his long day, so I figured I'd try again Saturday.
This afternoon (Saturday), Charlie came out, and while I was feeding him a few superstorms I noticed his right eyelid was once again swollen (1st pic), though I didn't notice any debris in it, I flushed it and moved him to a temporary holding bin to keep an eye on it. A half hour later the swelling had gone down quite a lot (2nd pic), and was completely gone within the hour.
I would really rather prefer this not keep happening, so I was hoping you might have some advice for me...I haven't noticed any changes in the tank recently (power outages/temp spikes/etc.) so I don't know why this has happened twice in just a few days.

Specs:
Tank - 4'x2'x2' DIY enclosure, with vents on both ends, some live plants in clay or plastic orchid pots (2 snake plants and a pothos), some isopods and springtails
Heat - DHP controlled by an Exo Terra thermostat - hot spot 110F, warm side mid 90s, cool side mid 70s, his preferred hiding spot is under the slate in the front right corner and is usually in the mid 80s
Light - Arcadia UVB 12% for 9 hours (covers about 1/2 the tank, against the back wall), LED for a 12 hour light cycle
Humidity - usually mid 50s (I live in a half basement so it sometimes spikes a bit higher, especially after I water the plants)
Substrate - mainly a mix of cypress mulch and coco husk, with a small amount of eco earth/charcoal/sphagnum moss leftover from a previous mix, some leaf litter
Food - mix of cat or dog food with veggies, some canned snails/phoenix worms and a small amount of fruit every 6 days usually 1-2 tbsp, insects as a treat (superworms, hornworms)
Supplements - dusting of calcium almost every feed, multivitamins every few feeds, calcium with D3 every few months

Please let me know if there's any other information you need!

Hi there and sorry I didn't notice your post until today. I am so sorry that your skink keeps having issues with it's eyes. Not fun at all. Is it still? If so, I would suggest another call to your vet. I would let them know even with the flushing, it still keeps happening. Not to worry you to much, but they may need to explore the eye further and make sure there isn't any other sort of foreign body in the eye or third eyelid. Is the skink on pain meds or anything? That looks sore. I wish you the best of luck. Let us know how it is going or what the vet says.

Thank you! His eye reacted three times in four days (each day he spent in his tank, the one day it didn't was the day I kept him out to take to the vet) but the swelling always went down within an hour of pulling him out and flushing it. I got tired of doing this, and worried about long term side effects, so I decided to put him in a temporary tote (placed on top of his tank so he still has heat), to keep a close eye on him, and to see if it would keep happening. Since then he hasn't had a reaction, so I am assuming it's something to do with my substrate mix (especially since I sometimes see coco fibre around his eyes and the vet found the coco hair in his eye), I'm just not sure why it took over a year to react like this.

This weekend I am tearing apart his tank and sanitizing everything I can with chlorhexidine (just in case it was bacterial or something else that could be transferred), then replacing the substrate with just cypress mulch, no coco of any kind. I will keep a close eye on him for a bit after, but hopefully that will fix the issue, if not, I'll take him to a different, reptile certified (ARAV) vet a little over an hour away from me.

Hi there. It very well could be just the substrate causing the issue. Good job noticing that this may be the case. I hope once everything is changed over that you won't have any more issues.