Pro Tip: Don't run RO/DI unit in reverse - high PO4

[Garf]

So I have had an unexpected diatom bloom. Thought I should test phosphates, so I ordered a Salifert kit. While I was at it, got the NO3 also, as I wasn't happy with the API nitrate test. Sunday ordered from Amazon, arrived this morning. Gotta love Prime.

 

Surprised when I tested, got .25 on tank water. Explains the bloom and why my hammer frag isn't fully opening. Shrooms, rfa's love it though. I have been feeding a bit more, to get my nitrates up, as API kit gave me the subjective reading of somewhere north of 0. Was still surprised about the PO4 though. Tested the boxed water, and PO4 was zero. Pulled out my TDS meter. I swore I used it a few months ago (wrong!), and reading was zero. That was why I didn't replace my membrane or filters on my RO/DI unit when I got them early this year (wrong again). Turns out I ordered new filter set back in September. Who knows when I tested TDS last, unit was dead, drained batteries. Bought new ones, tested, and reading was 200. Hell, my tap water doesn't even test that high. 

 

So I went to the source, and pulled out the unit to make some water. At some point, it appears I swapped the input and output lines. I imagine running water through the system in reverse can't be good for it, so I replaced the membrane and the filters. TDS reads 0, PO4 tests at 0. 15% WC and tank water shows .2 PO4.

 

So I am not sure how phosphates interact with other params. Does it need to be slowly reduced? Should I just make more water changes this week, or stick to my weekly schedule? Two clowns are doing fine, a few LPS frags in the tank, and only my hammer seems unhappy.