I have used the standard dosage of 1 to 1.5 measured teaspoon per actual US gallon of water (not nominal volume - no tank actually holds its nominal volume*) with a huge variety of fish. That definitely includes Clown Loaches, Kuhli loaches, and other species in the family, plus myriad catfish (multiple families), Tetras, Rasboras, Barbs, Cichlids (from rainforest to Rift), Anabantids, just about anything i have kept myself.
We have been in this house >25 years, plus the prior 9-10 years in our former home, during which time I have had no, repeat no, outbreaks of FW Ich outside of QT. In that period, the tan census has varied from 12 (during moving from the old house to this one) to over 40. I am totally compulsive about QT as I operate many linked systems of tanks (circulating ranges) and cannot afford infectious diseases, especially easily treated ones such as Ich.
*I do know the actual volume of all my tanks. The one time I use buckets is in set-up, to measure working volume. Otherwise I pump water to where it is needed, and generally remove by vacuum (Python). And, yest, I do have a separate Python for QT, along with all the other needed equipment for QT. If you use nominal volumes, you may well OD on many meds.
Substrate and decor volumes can radically affect working volumes. My "rocky" tanks can easily have half or less of the nominal volumes - one reason I use so many "sumps" or refugia. I need the working water volume to be far more than that available in the display - I learned that from public aquaria many decades ago. My Malawi mbuna setup required two veggie filters - more for volume than anything else, but I get higher O2 levels with the reverse and same light cycle veggie filters and eat a lot of nitrogen at the same time. My Tanganyikan breeding systems have similar fry and veggie filter "sumps" for the same reasons. The Rainbows have even larger ones as they breed more profusely. I really need to know real volumes of all the systems, even if most/none have never seen any meds.
Where's the fish? - Neptune