Ok, your ph will be an issue. The same thing happens with minocycline (higher the ph, less effective the med is). I dont keep tetras, so I trust Mumma's advice. Full salt 'typically' would be .3% (11.4grams/g or almost 3tsp/g) but some consider .5% or even as high as .9% to be full salt in fw
fish. I would stick to .3% as general rule of thumb- you can always increase it if need be but I honestly would not go beyond .5%.