[Stones]

I purchased the same doser and couldn't be happier. After one little adjustment mine has been working perfect since the get go.

I noticed that these dosers work better on speed 4 for a short duration of time rather than speed 3 or less for a longer period. Mine was heating up the peristaltic tubing and causing a black film to form on the surface and flake off down towards my sump. Once I adjusted the pump interval to be shorter for a higher speed, it's been working great.

Another observation I had with my doser was that the dosing amount listed in the manual wasn't even close to what my actual doser was pumping. I was using a shorter length of tubing than what the book said so my pump was actually pumping way more fluid than the max dosing rate listed in the book. I simply collected all of the fluid being dosed from the 3 pumps in containters and measured it after a full 24 hour period. I took 3 or 4 days to get the dosages figured out proprely but if you went by what the manual said, you are likely overdosing. Overdosing Ca or Mg isn't such a big deal but an overdose of Alk will lead to a rapid decline in all of your corals health.

Hopefully you can figure out what the problem is but I'd start off by collecting all of fluids being dosed to make sure that is accurate and also check your tank parameters as well. My guess would be your Alk levels are too high.