Hi and welcome to the forum.

you have quite a few problems here. Your tank is tiny for 3 milks.

Get pedyalite or whatever similar you have, look for electrolyte solution that is not flavoured or coloured.

Do a water bath, 5 parts of water, 1 part of water, keep a frog in there for about 20 min, water level no higher then frog chin.

After place it in a quarantine tank - wet papertowels, all 4 sides covered, foliage. find a vet and get it tested for parasites asap!

your water, can you pls specify what you meant by mineral spring bottled water. Is it spring water or mineral water? At any rate you better get water conditioner and use it for your tap water instead.