For the past say month or so the clown tank has been showing signs of discomfort followed by a few whitespot, no more than 2-3 spots per fish on the body not the gills, no biggy, up the temp goes and some added airation and it usually clears (we are talking about 3years ago when they last got an outbreak). So the spots seemly disappear after a few days, temp stays up along with airation for the following couple of weeks just to make sure everything is all clear but no, the fish still show signs of discomfort and now darn spots are back

Im not that comfortable with using medications without it being completly necessary. I picked up a couple of bottles of Malachite Green, enough to dose the tank 4 times at half doses but Im pretty sure this will completly ruin my seeded filters and last time I used this stuff I lost 3 5inch clowns; anyone else got any ideas what else I can do apart from treatments? Is there a chance it will shift without treatment apart from heat?? Or is there a treatment I can safely use that will not affect the filters??
Tank- 5x1.5x2
Ammonia 0
Nitrite 0
Nitrate 40ish - trying to put off water change incase Ich flares up
pH 6.8-7 - It moves between these values
Filtration - Eheim wet and dry, Fluval 303, 2 Fluval 3+, 2 aquaclear powerheads
Temp 30-31 degrees C
No new additions, plants or anything since the tank was setup so no idea how this got into the tank in the first place, must be that darn welsh water

Adding two more powerheads this evening and another heater to make sure water temp doesn't fluctuate to much.
Anyone... help??

Ashleigh