By Patchin Curtis (extracted from a PVAS forum thread)
Barbie Fiorentino gave a fascinating talk on Loricariidae in which she described her protocols for treating her tanks twice a year with ProForm-C to kill off various parasites to a manageable load for the fish. Barbie has a centralized water filtration system, so pathogen management is especially important.
ProForm-C is a concentrated form of formalin and malachite green developed specifically to treat ich on scaleless catfish which can be particularly sensitive to malachite green. For this reason, the formulation utilizes malachite green chloride instead of the more common malachite green oxalate which is more toxic to scaleless fish.
Barbie treats all her tanks with ProForm-C twice per year. To treat, she first removes any carbon, rinses filters, and performs a large water change to reduce the dissolved organics as much as possible which increases the effectiveness of the medication. The closer this initial water change is to 100%, the more effective the treatment will be. Given the potential toxicity of ProForm-C, it is important to follow the instructions to the letter and to carefully observe the fish during treatment. Use 5 ml (1 tsp) per 50 gallons of tank or pond water. Barbie repeats the treatment after water changes for a total of 3 consecutive days.
ProForm-C will set your filters back but will not completely kill off the denitrifying bacteria. It is important to rinse your filters before, during, and after treatment to remove the maximum number of parasites possible. It is unlikely that 100% of the parasites will be killed, but they will be very significantly reduced to a load that should be easily supported by healthy fish in good tank conditions.