ACF potential infection or death extremely worried

[Froglover3947]

Hello, recently I have done a full tank water swap along with cleaning out the sand because of brown algae starting to grow. My ACF is about 7 years old and ever since the water change he has been hiding in his corner behind his log for most ever since, I have a shorter day cycle and he ate the last two feeder guppies but will not eat his regular invert aquatics frog bites. I noticed he has a cloudy eye and some black speckles on his back. Can anybody please help me out I am very worried for him?
General hardness at 0
KH at 40
Ph at 6
Nitrite 0
Nitrate 0
Tank is 20 gallon plenty of space for him and I have 2 Anubias nana’s in there looking very healthy and green

 

[bcfishtanks]

I'm sorry to hear about your frog. I don't know much about frogs, but I'll try to help based on what I know about aquariums:

What do you use to condition your water?
Have you changed product brands recently or fed him anything he wouldn't usually eat?
Has he been in this tank his whole life?
Did you lose power or anything recently that could have affected the machinery of the tank?
Did the feeder fish seem in good health?
Do you have an ammonia reading?

Many people on here recommend the API liquid test kit, as it gives more accurate results and tests for ammonia. The test strips can be inaccurate. If you can't afford the test kit, local stores will usually test your water for you for free.