The active ingredient in Flourish Excel is glutaraldehyde. It is known to kill fungus - JAMA Network | JAMA Dermatology | Antifungal Activity of Glutaraldehyde in Vitro Could I use it in conjuction with salt baths to treat a fungal infection?
My understanding is that excel was one of the few products you could use in axolotl tank. I've used half dose for a year in one of my axolotl tanks and they were healthy and breeding.
Axolotl Sanctuary
Read the Plant Care section.
I am going to agree with the advice given by everyone here. But I am curious to know why you were using it for a year?
Flourish excel is a liquid source of carbon for plants. I use it almost all my planted tanks. Its harmless to fish and my axolotls havent shown any ill effects of its usage. In fact my axolotls didnt get the fungal infection until I stopped using it.