Hi Irf
It's been my experience that MelaFix can be very effective in curing bacterial infections.............or not. From what I have seen, if it's going to work it will result in a dramatic change for the better within just a few days time. If no benefit is evident in that time, it's usually best to move to something more potent.
Instead of using MelaFix, I sometimes mix my own which I call Melafake. To make it, mix 1/4 tsp. 100% pure tea tree oil (from a health food store) with 8 TBS. dechlorinated water. Shake very well and use it as you would MelaFix. Shake well again before each use.
Pure tea tree oil is a very light, thin substance which will mix with water, if well shaken. When Melafake is added to water intended for use as part of a water change the force of the water coming out of the tap will further agitate it and mix it with the water. It will then mix with the tank water the same way MelaFix does.
Pure tea tree oil costs me $6.95 for 1 fl. oz. at the health food store. Compare the price of making your own with the price of MelaFix and you will see that there can be a tremendous savings.
Another, probably simpler solution, is to buy Pond Strength Melefix and dilute it appropriately. Either way, I would recommend using a much smaller dosage than the instructions on the bottle call for.