Increasing ORP Values?

[Aspect]

Hello, my tank has running ORP consistently in the low 280-320 range over the last 6 months, and now in the last month in has been climbing and is now in 420 range. Besides testing different light intensities out I haven't changed anything and only added some fish/coral. What could be the cause for this and what can I do to drop it?

 

[Randy Holmes-Farley Verified Community Expert]

Algae growing in the probe can raise apparent ORP.

That said, ORP NEVER gets high enough to warrant action to lower it if you are not dosing oxidizers such as ozone or permanganate.