Why is my ORP so high?

aaron186 · Mar 16, 2025

I’ve been monitoring my ORP for the past 4 months since I plan on adding ozone to my tank and wanted to get a baseline ORP. It was running 200-300 for the first 2 months but 2 months ago it shot up to 550 and has stayed there.

I thought it might be probe issues so I cleaned it. I bought a standardized solution to 222 and it’s reading 270 so it seems like it’s at least functioning.

I’ve several large volume water changes without much change from the 500-550 range. I’m doing routine auto water changes of 1L daily.

I just tested my RODI and it’s 380-400 so I think it might be my water? Is this normal for RODI? I have a 7 stage BRS unit and I’m changing my filters.

I’m dosing All for reef (alk 8), use Tropic Marin pro reef salt, and also dose TM carbon dosing elimini NP. My nutrients and numbers are pretty stable.

My tank is growing and doing well. But I’m reluctant to start ozone with my orp appearing to be so highl

Any one with any insight why my ORP might be elevated?

RockBox13 · Mar 16, 2025

Are you running a skimmer? Do you have a refugium? What kind of flow do you have in there?

aaron186 · Mar 16, 2025

RockBox13 said:
Are you running a skimmer? Do you have a refugium? What kind of flow do you have in there?

Yes I have both. I’m running about 5x flow through sump. Fuge has power head in there to gently tumble chaeto and my skimmer section also has a power head in it (a Nero 3) that is under my dosing tubes. Skimmer is DC powered Reef oct and on the middle setting and hasn’t been adjusted recently

RockBox13 · Mar 16, 2025

aaron186 said:
Yes I have both. I’m running about 5x flow through sump. Fuge has power head in there to gently tumble chaeto and my skimmer section also has a power head in it (a Nero 3) that is under my dosing tubes. Skimmer is DC powered Reef oct and on the middle setting and hasn’t been adjusted recently

I think that you’ve got great oxygenation and you’re running a good system. Let’s say that ORP meter is off by 50 like it seems. That means you’re probably at 450-500mv. Definitely the higher end, but nothing excessive. I’ve run ozone on systems with a good ORP before and it’s definitely got its benefits, but no drastic changes on systems that are already so well oxygenated. Not to discourage you from using ozone, but what are you looking to improve upon by running it?

aaron186 · Mar 16, 2025

RockBox13 said:
I think that you’ve got great oxygenation and you’re running a good system. Let’s say that ORP meter is off by 50 like it seems. That means you’re probably at 450-500mv. Definitely the higher end, but nothing excessive. I’ve run ozone on systems with a good ORP before and it’s definitely got its benefits, but no drastic changes on systems that are already so well oxygenated. Not to discourage you from using ozone, but what are you looking to improve upon by running it?

Water clarity so I can eliminate the carbon reactor and not need the maintenance of changing it out

aaron186 · Mar 16, 2025

RockBox13 said:
I think that you’ve got great oxygenation and you’re running a good system. Let’s say that ORP meter is off by 50 like it seems. That means you’re probably at 450-500mv. Definitely the higher end, but nothing excessive. I’ve run ozone on systems with a good ORP before and it’s definitely got its benefits, but no drastic changes on systems that are already so well oxygenated. Not to discourage you from using ozone, but what are you looking to improve upon by running it?

So you’re saying it’s safe to run ozone on a tank that already has an ORP of 500ish? Any clue why my RODI ORP is also high at 400?

RockBox13 · Mar 16, 2025

I believe it’s safe. Clarity is insane and you should see some of the best polyp extension you’ve ever seen. I get that you want to eliminate maintenance and I’m all for it. It’s just that you’re probably going to trade changing carbon for changing out the dryer beads in the air dryer that goes before air enters the o3 chamber. It’s also notoriously difficult to keep an ORP probe clean and calibrated enough as you can already tell.

Miami Reef · Mar 16, 2025

If you aren’t using ozone, ignore the ORP reading.

If you plan to use ozone, ORP helps you prevent overdoses. Only allow ORP to rise about 30mV above the initial reading.

You should still use carbon on the skimmer output to break down toxic byproducts like bromate, but less carbon is typically needed and lasts much longer since it’s only used as a catalyst.

Miami Reef · Mar 16, 2025

aaron186 said:
I’ve several large volume water changes without much change from the 500-550 range. I’m doing routine auto water changes of 1L daily.

Water changes and RO/DI don’t typically have an effect on ORP. Be aware that ORP is uncharted territory and not fully understood, even by fully experienced chemists. It’s VERY complex.

I’d suggest bleaching the probe tip for 30 min (rinse after) and add it back to the tank. It can help reset the probe by removing the algae or film on the tip.

RockBox13 · Mar 16, 2025

Miami Reef said:
Water changes and RO/DI don’t typically have an effect on ORP. Be aware that ORP is uncharted territory and not fully understood, even by fully experienced chemists. It’s VERY complex.

I’d suggest bleaching the probe tip for 30 min (rinse after) and add it back to the tank. It can help reset the probe that is giving weird readings.

Did you always run an air dryer with your ozone generator? I’m assuming he will be putting the o3 into his skimmer as well here.

Miami Reef · Mar 16, 2025

RockBox13 said:
Did you always run an air dryer with your ozone generator? I’m assuming he will be putting the o3 into his skimmer as well here.

Yes. Air driers make it more effective.

It’s just a canister of silica beads that can be recharged with a regular oven. I only used ozone once a week, which was enough to clear the water.

RockBox13 · Mar 16, 2025

Miami Reef said:
Yes. Air driers make it more effective.

It’s just a canister of silica beads that can be recharged with a regular oven. I only used ozone once a week, which was enough to clear the water.

I just wanted out friend here to know that the maintenance on the beads is a big hassle all the time and definitely more work than changing carbon every so often.

Miami Reef · Mar 16, 2025

RockBox13 said:
I just wanted out friend here to know that the maintenance on the beads is a big hassle all the time and definitely more work than changing carbon every so often.

Not necessarily. Using an air dryer is optional. They sell large quantities of beads, so you can easily put the exhausted beads in a baking tray, refill it the canister, and bake the collection at your convenience.

It’s much easier to bake a large batch infrequently than small batches often.

aaron186 · Mar 16, 2025

RockBox13 said:
I just wanted out friend here to know that the maintenance on the beads is a big hassle all the time and definitely more work than changing carbon every so often.

I have one of those plug in dryers that are stupid expensive. A friend who got out of hobby gave me his for a nice dinner