Use of Ozone

[Queen City Reefs]

So, I've been contemplating using Ozone in my 310 Gallon Mega Matrix Aquarium. Why? Well, I love trying things that I've never tried before and want to see for myself, if there are any benefits (aside from water clarity).

I've always heard people say to run ozone w/ controller and base when it runs based off of your ORP. Well my ORP currently reads over 400. At the moment of writing this, it reads 457. I believe that is where normally people have stated to have Ozone turn off.

So you see where I am going with this? Should I still use Ozone with that ORP Reading? If so, what do I need to shoot for when using it?

 

[Randy Holmes-Farley]

I expect the only change you will observe with ozone is water clarity.

Here is my recommendation on ORP with ozone. In your case, I’d aim for a small ORP rise, say 10 mV.

Ozone and the Reef Aquarium, Part 1: Chemistry and Biochemistry by Randy Holmes-Farley - Reefkeeping.com

Ozone and the Reef Aquarium, Part 2: Equipment and Safety by Randy Holmes-Farley - Reefkeeping.com

Ozone and the Reef Aquarium, Part 3: Changes in a Reef Aquarium upon Initiating Ozone by Randy Holmes-Farley - Reefkeeping.com

From the second one;

​

In dosing ozone to a reef aquarium, the more ozone that is added to the system, the higher the ORP will rise. I do not agree with assertions that some aquarists have made that higher ORP means cleaner or "better" water. If ORP is going to be used as a guide to prevent overdosing of ozone, however, then some commentary is needed on ORP's target levels.​

Without using ozone, reef aquaria vary widely in their ORP values. Some aquarists report values in the upper 300's of mV, while a few even claim over 400 mV. My reef system's ORP runs in the middle to upper 200 mV without ozone. Some claim even lower values. Part of these ranges may relate to complications in calibrating ORP measurements and equilibrating ORP electrodes (a process that can take days), and part to the fact that ORP varies with pH, but much of it likely relates to real aspects of husbandry that change the base ORP that an aquarium attains.

Before going on to discuss ORP and ozone, let me relate one issue that may impact how strongly aquarists should rely on the accuracy of ORP. As mentioned above, ORP is not a simple equilibrium measurement. The probe itself may have a memory of what it has previously been exposed to, and that may impact readings, EVEN IF it seems to be properly calibrated. That memory may relate to organic and inorganic materials attached to the platinum surface itself. For example, if I calibrate my ORP probe (in Pinpoint 400 mV fluid), let it equilibrate in my tank for many days and then put it back into a new batch of the same ORP calibration fluid, it reads the value it is supposed to in the calibration fluid. But after returning it to the tank's water, the tank's ORP reads 25-30 mV higher than before the probe was put into the calibration fluid, and that boost lasts for days. Likewise, putting the ORP electrode into very high ORP solutions (the ozone reactor's effluent, for example) seems to impact the electrode in the opposite direction, dropping the tank's observed ORP by about 25 mV when measured more than a day later (and much more when measured right away). The take-home message is that aquarists should not interpret small, absolute ORP changes as meaning anything in particular, and they may, in fact, simply reflect changes happening to the ORP probe itself, and not changes actually occurring in the water.

Upon initiating ozone use, some aquarists, like me, see only a small rise in ORP even at recommended levels of ozone. My ORP doesn't rise above 330 mV, for example, and some aquarists' tanks are still in the 200 mV range even after initiating ozone. Others, presumably those who start with a high ORP value, although that may not be the only factor, easily drive their tank's ORP too high if it is not controlled.

So with all that background discussion behind us, here are my recommendations for ORP monitoring and ozone control in reef aquaria using a properly sized ozone generator that appears to be working, and a properly calibrated ORP meter:

If the ORP never seems to rise above 375 mV after initiating ozone, do not worry about controlling the ozone or the ORP. Just let it run full out. Also, do not worry about needing a larger generator, assuming it has driven up the ORP by at least 25 mV above where it was before adding ozone. It is likely accomplishing the necessary tasks (such as making the water clearer). Only if some other aspect of ozone use is unsatisfying (e.g., lack of water clarity) would I look for other options such as a larger ozone generator or a better contact chamber.
2. If the ORP starts above 375 mV, or rises there during ozone use, using an ORP controller would be valuable to prevent the ORP from rising too high. Use the controller to shut off the ozone when the ORP rises too high. Another option would be to shut off the air flow to save the dryer's media, but be sure that water cannot flow back into the ozone generator if the air stops. I would set the ORP target somewhat above the baseline ORP in the absence of ozone - at least 350 mV, maybe 400 mV, but never above 450 mV.

 

[Randy Holmes-Farley]

Ignore the weird format issues that I cannot fix on a phone.

 

[Miami Reef]

I would consider making a bleach solution of 10:1 water:bleach and let the probe sit there for 10-20 minutes. Then rinse off and place back into the tank.

It’s not plausible for a reef’s ORP to be above 400 without oxidizers. I hypothesize that the ORP readings will settle down after the soak. Sometimes things can grow on the probe and artificially raise the ORP.

Bleach doesn’t damage the probe, and I think you have nothing to lose by attempting the bleach soak. I and other ozone users do it.

It just takes a few days for the reading to become accurate again. I’d try it out.

A few tens of a raise is all you need for water clarity.