Regarding readings if 0.03…
I repeatedly had problems when I tried to manage it at that low level. Sometimes because I’d end up at 0.00 but other times not. Very unhappy corals and In the worst case dinos. I always figured it was test error, which it could be, but I also stumbled on something interesting recently.
I was measuring every 12 hours and found this interesting trend (below). In my tank it appears PO4 swings between morning and night. At first I chalked it up to test error but the pattern kept repeating. This same pattern has continued for another 3 days so I think it might be real (there are reasons it might not be). I have some ideas what might cause this, but it probably doesn’t matter. It does reinforce to me that the higher target range I’ve been using for a while is a good idea. The corals have appreciated it which was really all I needed to know. I haven’t followed any of the trident NP users to see if they see the same thing.