Rowaphos raising ORP 100 points?

ReefLaw · Oct 13, 2021

I recently started using Rowaphos two weeks ago in my 120 gallon reef system in order to lower phosphate down from .35. However, my starting ORP was 315 (calibrated probe) and has slowly risen to 415 and is settle there now. I'm using about 3 tbsp of rowaphos in a media bag in my sump. Has anyone had this experience before or can offer an explanation?

blaxsun · Oct 13, 2021

I use about 250ml of Nyos Phosi-EX (similar to Rowaphos) every 6-8 weeks, which is considerably more than you indicate. I don't think I've every seen a ±100 fluctuation when turning off my carbon/GFO reactor, though. Have you added or upgraded any other equipment?

Randy Holmes-Farley · Oct 13, 2021

I do not know if the effect is real or a test error, but I can think of two clear reasons why it would raise ORP.

1. Dissolution of substantial ferric iron Fe+++ from GFO should raise ORP, just like adding ferrous iron (Fe++) should lower ORP. The ratio between Fe++ and Fe+++ is governed by ORP (or, alternatively, the ORP governs the ratio) assuming they are in equilibrium with the whole ORP menagerie of redox active chemicals in the tank.

2. Binding of organics to GFO may tend to raise ORP.

Just remember to not assume higher ORP is "better" than lower ORP.