What does a continuous drop in ORP between water changes mean?

[xxxenmsy]

My SPS tank has been established for about 6 months, and I’ve noticed a very consistent pattern with my ORP readings:

The day after a water change: ORP peaks at around 380–390 mV.

Daily trend: It steadily drops by about 10 mV each day.

The day before the next water change: It hits a low of around 330–340 mV.

This cycle repeats predictably with every water change interval.

What does this steady daily drop indicate? Does it mean I'm overfeeding, or is it just the normal accumulation of dissolved organic carbon (DOC)?

 

[Justfebreezeit]

Id assume normal degradation between water changes

Unless you are running something like ozone its unavoidable id imagine

 

[Dan_P]

My SPS tank has been established for about 6 months, and I’ve noticed a very consistent pattern with my ORP readings:

The day after a water change: ORP peaks at around 380–390 mV.

Daily trend: It steadily drops by about 10 mV each day.

The day before the next water change: It hits a low of around 330–340 mV.

This cycle repeats predictably with every water change interval.

What does this steady daily drop indicate? Does it mean I'm overfeeding, or is it just the normal accumulation of dissolved organic carbon (DOC)?

That seems like a small change and not likely something that can interpreted. You would need a test like Triton’s NDOC to measure the DOC before and after a water change to determine if there is a connection with ORP values.

 

[EnterName]

ORP is weird...
Mine is really low and drops with water changes. I'm using Nyos Pure salt and highly pure RO/DI. Activated charcoal doesn't help either, it's sometimes appearing to lower ORP even further
Nutrient levels are really low, but I could imagine that DOC levels are high as I rarely do water changes.