[Delphinus]

Someone at RC has suggested to me maybe the problem is that the sulfur interferes with the test kits.

If that's the case, it could explain a LOT.

However if that's the case then I don't know how to tell if the unit is working, or when it's time to increase the flowrate.

Hopefully my nitrate monitor arrives back soon. American Marine did confirm it was faulty, and repaired it and sent it back. The only thing is it took almost a full two weeks to get to them (and this was the "U.S. Parcel Expedited" service from Canada Post), and so I would expect it will take at least as long to return. Been about a week and a half since they sent it back so with some luck it does come this week. At least I feel a little vindicated on that one, he had told me that of the hundreds they've sold I was the only one to complain it wasn't working, then when he looked at it he confirmed it had a wiring fault. Anyhow at least it's been fixed but it would be nice to have the thing back soon!!!