This is what we use here at the store and at Cory's fish room to treat every fish we come into contact with. For us we've never had problems using it with inverts, scaleless fish, and plants.
Commonly used to treat:
Ich (Ichthyophthirius multifiliis)
Velvet (Gold Dust Disease)
Saproleniasis (Cotton Wool Disease)
Protozoan Caused Diseases
Contains:water, formaldehyde (<5%), methanol (<2%), malachite green chloride (<0.1%)
Add 1 teaspoon (~5mL) for every ten gallons. For best results always treat in a separate quarantine or hospital tank and remove activated carbon. Change 1/3 of the water before each additional dose of Ich-X, dose every 24 hours until symptoms resolve.