If the fish have whitespot (Ichthyophthirius) then you can treat it with heat. You raise the temperature to 30C (86F) and keep it there for 2 weeks.
Increase aeration and surface turbulence to maximise the oxygen level in the water.
Clean the glass, do a 75% water change and gravel clean the substrate before raising the temperature. Only raise the water temperature 2-3 degrees C each day until the temperature gets to 30C.
If you use heat treatment you do not need to use medications.
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If you want to use medications be careful what you use and use a medication suitable for scaleless fishes like catfish and loaches. If the medication has no instructions for use with scaleless fish then use it at half dose.
To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.
There is a calculator/ converter in the "How To Tips" at the top of this page that will let you convert litres to gallons if you need it.
Remove carbon from the filter before treating or it will absorb the medication and stop it working.
Wipe the inside of the glass down, do a 75% water change and complete gravel clean. And clean the filter before treating.
Increase surface turbulence/ aeration when using medications because they reduce the dissolved oxygen in the water.
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There is more info about whitespot at the following link. The first post on page 1 and the second post on page 2 are worth reading.
http://www.fishforums.net/threads/what-is-ich.7092/page-2
