The HT has a capacity of 1880 litres. I was in the same opinion as you with respect to the amount of Peroxisane used, but this was instructed to me directly by the people at perexisane.
You may have a point with the weekly filter change out. The dealer who sold us the HT is promoting these 1 micron disposable filters that are suppose to last 3 months. I will do as you suggested, change the filter weekly, I hope this help.
The filtration is set same frequency/duration as yours, plus each time that I am outside the vicinity of the HT, if the pump is not running, I start it up. So it is getting plenty of daily filtration time. The people at peroxisane mentioned that it was preferable to run the pump at low speed 24/7. This is, I think, somewhat taxing on the equipment.
I think our well water may be the possible culprit. As I mentioned in my first tread, to refill the entire tub we get the water trucked in (city water), but the make up water is supply from the well. It seems that I am having water problem each time I do that.
I am looking at using Aqua-Finesse. I will make a decision in the next couple days. In the mean time the tub is ready for another refill.
I will let you know how I am making out.
Jacques