Dechlorinated tap water is fine for frogs. Some owners think they are going one step further and use other water sources thinking it's going to be better and accidentally make it worse.
Water bottling companies have to meet certain city codes of purity and how they go about it can alter the water so it's unsafe for frogs. The bottle might say "spring" but it's rarely pure spring and many times there is some processing involved.
In the case of Cristal Geyser think the problem is aggressive filtration to reach very low mineral contents. Then the water, although safe to use for human drinking, becomes unsafe for frogs. In that water frogs would loose minerals to the water creating chemical imbalances that affect the frog's physiological processes and create a health issues similar to when R/O or distilled water is in use.
So my recommendation is to use treated tap for your frog. If local water is hard and leaves water spots on glass when spraying can use distilled for spraying but avoid spraying frog directly with it.
If this was the cause or it contributed to frogs issues it should get better; but be aware it could take some time since frogs heal slowly. Good luck

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