use full 100% holtfreters solution which is 3.46g salt, 0.05g potassium chloride, 0.1g calcium chloride, 0.2g bicarbonate of soda, also add 0.2g magnesium sulphate, it is easier to mix the solution in two parts so the salt/potassium/calcium/magnesium in 0.5 litre and the bicarb in 0.5 litre, this is because once the bicarb and the calcium chloride mix calcium carbonate is formed so it is easier to add them separately, it is also easier to make up larger amounts due to chemical quantity's and ease of measuring. this is to resolve fungal issue
feed small food types such as bloodworm/brineshrimp/mysis/krill etc.. feed at night time and leave in overnight the do water change following day.
ascorbic acid (vitamin c) can be added into the holtfreter solution as it may help encourage appetite and will also convert some calcium carbonate into calcium ascorbate which is easily absorbed as a source of calcium, can be added at 0.1g per litre but better to start at 0.05g per litre.
frozen brineshrimp/krill/cockle/mussel have vitamin A which is required in salamander and other amphibian diets, some pellets also contain the required vitamins as well.