ORP decreasing when using UV light?

Acalin · Mar 2, 2022

Hello all,

Yesterday I got a UV sterlilizer for my tank (as I am fighting some algae) and upon installing it and turning it on, my ORP readings started dropping.
Below is are 3 screenshots from my APEX (first one showing last few days and second a zoomed in for the last 24 hrs, while the 3rd one is just an overlay with my PH readings as I was curious if PH was acting abnormal, but it doesn't seem so).
The decrease coincides with the time I switched on the UV sterilizer (around 5: 45PM). It looks like it plateaus around 270 range, but I was wondering if the decrease in ORP is a good sign or a bad sign, as far as algaes (dinos) go.

As always, thank you!

Sean Clark · Mar 2, 2022

I would correlate the drop in ORP to the new equipment being added, not the UV light but the housing. All of the new surface area that has been added to the system can drop your ORP. I will bet that it will slowly come back up to the 300ish range where it was before.

Nothing to worry about.

I would bet that the dip on the evening of Feb 28 was a water change or some other kind of maintenance.

Acalin · Mar 2, 2022

Sean Clark said:
I would correlate the drop in ORP to the new equipment being added, not the UV light but the housing. All of the new surface area that has been added to the system can drop your ORP. I will bet that it will slowly come back up to the 300ish range where it was before.

Nothing to worry about.

I would bet that the dip on the evening of Feb 28 was a water change or some other kind od maintenance.

Thanks for the quick respone, Sean!
Yes, evening of Feb 28th was a bit of clean-up.

Randy Holmes-Farley · Mar 2, 2022

I can imagine a UV killing bacteria and breaking them open may drop ORP.

EugeneVan · Mar 2, 2022

My ORP reading is very stable and I ran VU 24X7. The only time ORP drop to 250 is when I was using H2O2 to spot treat a patch of green algae on the rock.