My Hanna LR has measured zero for a month now. I have a bit of rowaphos in a mesh bag in a submersible air uv/pump. I haven't changed it in 6+ weeks so I'm sure it's spent. I feed unwashed mysis shrimp and a little reef roids every few days. I have some bubble algae growing, some gracilaria algae and some filamentous green algae growing in the display. Not much at all really. So..... Is my Hanna reagent bad or am I just below Low Reading into Ultra low. I must have some Phosphate right??!!?