ORP trending - dramatic changes after weekly maintenence

fryman · Oct 5, 2021

When I first setup my Apex on a new dry-rock start aquarium, ORP was just under 200. For the first 1-2 months it slowly trended up. When I added coral, it also started showing a daily cycle that seems to inversely follow pH.

For the past month or so, the orp trend has changed. Over the course of a week, orp gradually trends down (daily pH-related swings still present). While doing my weekly maintenance, orp quickly drops ~50 points. Then for the next 12-18 hours orp climbs steadily, reaching a new high value the day after maintenance. This week I peaked just over 400. Every week is a new record for this tank.

Is this normal? I assume it's ok since I am still within the "normal range". I expect it will eventually reach some max value and then repeat the same range-cycle weekly. Do other people see similar trends?

I have read Randy's article:

http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm

But honestly this just left me with more questions. Do we really know if orp is even useful? I was prepared to ignore it entirely but it's interesting to me this trend - orp obviously reflects something related to my weekly maintenence.

*edit* Weekly maintenance for me is:
1) blow off rocks using water jet, also suctioning blown off detritus through 1micron filter ~15 min
2) clean out skimmer
3) replace gac
4) dose iodine, iron, and PNS probio (bacteria supplement)

I do not do any water change during weekly maintenance. I do small water changes periodically over the week when feeding copepods.

blaxsun · Oct 5, 2021

It’s normal. There’s also a correlation between ORP and pH changes.

Hurricane Aquatics · Oct 5, 2021

It's completely normal. As your tank keeps aging and establishing the bacteria, your ORP will rise as it is able to oxidize waste better. Water changes are removing water that contains waste and replacing it with water that does not contain waste. So your ORP rises after a water change.

Mine usually stays around 350 to 370 as I do weekly water changes.

You can think of your ORP as the "cleanliness" of your water and system. However, it is ultimately the ability for your live rock, ceramic media, protein skimmer, etc. capacity to convert waste.

taricha · Oct 6, 2021

HurricaneSystems said:
You can think of your ORP as the "cleanliness" of your water and system. However, it is ultimately the ability for your live rock, ceramic media, protein skimmer, etc. capacity to convert waste.

I would fight hard to resist those interpretations. It's confusing more often than helpful. And swings in ORP are not swings in cleanliness or any other crucial water quality measure.

fryman said:
But honestly this just left me with more questions. Do we really know if orp is even useful? I was prepared to ignore it entirely but it's interesting to me this trend - orp obviously reflects something related to my weekly maintenence.

ORP of tank water is not a good indicator of anything unless you are adding a strong oxidizer or reducer compound.
Ozone, sure. feeding something with reducing compounds like vitamin C, sure. The up/down trends in those cases are responding mostly to the effects from those strong oxidizers or reducers. The bulk of things in tank water are just too weak of oxidizers or reducers for the ORP measure to tell you something important about your water.

Do you add anything during tank maintenance, or just like vacuum rocks & sand? There's a reservoir of reduced compounds in these low oxygen spaces.

fryman · Oct 6, 2021

I vaccuum out detritus from the live rock, and replace activated carbon in a small reactor. Only additions are iron and iodine supplements and bacteria (PNS Probio). I don't use ozone or UV or vitamin c in the tank.

I don't pretend to understand what this indicates exactly. It may not be a useful observation but I was just surprised at how significant (+75 to 100mv shift in < 24 hours) and predictable/repeatable it appears. It's definately correlated with mainteneance somehow.

taricha · Oct 6, 2021

fryman said:
Only additions are iron and iodine supplements and bacteria (PNS Probio).

Iron (and maybe Iodine) for sure can spike ORP down. Does that timing sync up with your observed drops?

Dan_P · Oct 6, 2021

fryman said:
When I first setup my Apex on a new dry-rock start aquarium, ORP was just under 200. For the first 1-2 months it slowly trended up. When I added coral, it also started showing a daily cycle that seems to inversely follow pH.

For the past month or so, the orp trend has changed. Over the course of a week, orp gradually trends down (daily pH-related swings still present). While doing my weekly maintenance, orp quickly drops ~50 points. Then for the next 12-18 hours orp climbs steadily, reaching a new high value the day after maintenance. This week I peaked just over 400. Every week is a new record for this tank.

Is this normal? I assume it's ok since I am still within the "normal range". I expect it will eventually reach some max value and then repeat the same range-cycle weekly. Do other people see similar trends?

I have read Randy's article:

http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm

But honestly this just left me with more questions. Do we really know if orp is even useful? I was prepared to ignore it entirely but it's interesting to me this trend - orp obviously reflects something related to my weekly maintenence.

*edit* Weekly maintenance for me is:
1) blow off rocks using water jet, also suctioning blown off detritus through 1micron filter ~15 min
2) clean out skimmer
3) replace gac
4) dose iodine, iron, and PNS probio (bacteria supplement)

I do not do any water change during weekly maintenance. I do small water changes periodically over the week when feeding copepods.