Formalin and Malachite Green combination is the most popular, cost effective medication for protozoan infections. Many companies sell this combination under various names. Proform-C being the most popular and Terminate being the most economical. There is also a product named Quick Cure which is 1.5 times stronger. When using this product adjust the dosage accordingly. More is not always better.

When NOT to use Proform-C/Terminate?
i) If the water is dirty or has algae and other suspended particles. Formalin uses up lots of oxygen to oxidize algae and dirt and will not have a chance to kill parasites. Oxidation process reduces the oxygen available for Koi and nitrifying bacteria. Oxidized algae and dirt will begin decomposing by other bacteria that will pollute water.

ii) Under 50*F, Formaldehyde is converted to a toxic product called paraformaldehyde that settles at the bottom. If you have stored your Profrom C under 50*F, simply throw it. If water temperature is 50*F or below, do NOT treat with Proform C or any other Formaldehyde product. Alternative treatment is plain Malachite Green.

iii) If water temperature is higher than 80*F, do not treat with Proform C/Terminate, At that temperature, water will not have enough oxygen to accommodate both Koi and Formaldehyde because Formaldehyde depletes oxygen by reacting with the organic compounds in water.

iv) If your water has salt or other chemical. Do NOT combine Proform C/Terminate and salt. Salt reduces the amount of dissolved oxygen present in water. Salt peels the mucus off Koi. Formalin will burn the skin/gills of Koi.

v) Do NOT use Proform C in the night if your pond has plants (plants use up oxygen in the night, dropping the pH).

vi) Doitsu or scaleless Koi are less tolerant to Formalin & Malachite Green. Do not use 1.5 times dosage suggested in Koi forums or by Koi dealers. Rather make significant water change to make the medication more effective.

vii) If fish are heavily infested and show breathing problems (hyperventialtion, gasping) they will not be able to withstand this harsh treatment. Reduce the recommended dosage by 1/2 or less. If you don’t know what is bothering them, first treat with Malachite Green alone (available as powder or liquid). This will reduce all but Costia infections.

viii) If you use dechlorinator containing sulfite/sulfonic acid or similar products (Pond Prime, Ultimate, Sodium thiosulfate, Chloram-X) use minimum amount and wait until they are depleted from the system. Formalin reacts with sulfite.

Malachite green present in Proform C is a known carcinogen. repeated usage may cause cancer.