Just do it slowly.I believe it's hard tap water. Gonna throw some peat and almond leaves in there.
Could be slimecoat or fungus. Would check ur water and make sure it’s cycled and nitrates are down below 20ppm. Also check ur water hardness. Looks more slimecoat than fungus but can’t be sure. I’d dose seachem paragaurd or salt or api fungus cure.