ORP 425 without ozone???

[nervousmonkey]

Howdy R2R! Question for the more knowledgeable folks out there...

I have a system that I frankly haven't paid much attention to over the last couple of weeks, ORP reading 425, stopped ozone on that system a month ago because it was making my skimmer go nuts. I was running ozone through a Reef Octopus reactor, ozotech with luft pump, but like I said, I haven't run that for a month. When I was running it, couldn't get ORP above 325, but now it's been rising since I turned off the O3... I also have biopellets running and have a Avast Marine purigen reactor that runs all the time. The probe is clean and I am pretty sure it is accurate.

What would cause my ORP to get this high? I know it's *probably* a good thing, but want to understand the chemistry behind it.

Thanks,

Lloyd

 

[Randy Holmes-Farley]

Firstly, ORP never gets too high in the absence of added oxidizers (ozone, peroxide, chloramine, chlorine, permanganate, Lugol's iodine, certain trace metal additives, etc.).

Second, low pH contributes to high ORP, everything else the same.

Assuming the result is not off due to algae growing on the probe or miscalibration, high ORP generally results from low organics. But I do not generally assume that higher ORP is better.

While you did not mention it, I expect that running carbon (GAC) is a mixed result, with organics being bound, but highly oxidizing species decomposing on it.

This has a lot more (way more than you may want) on the chemistry of ORP in a reef aquarium:

ORP and the Reef Aquarium - Reefkeeping.com
http://reefkeeping.com/issues/2003-12/rhf/feature/index.htm

and here is the simplified section from it:

Simplified ORP

Imagine a reef aquarium as a vast battlefield. No, more vast. Much, much more. OK, that's ORP. That is, ORP is a measure of who is winning and who is losing the battle. The battle is never won by one side or the other. As an aquarist, you do not want it to be, or else everything in the tank would be dead. In other situations, such as the purification of tap water for drinking, allowing the oxidizers to win is fine. A high enough ORP (650+ mv) can kill most bacteria in a few seconds.

On one side of this aquarium battle there are the oxidizers. They all want to get electrons, and they rip them off of the bodies of the enemy. The foot soldiers of the oxidizers are oxygen molecules (O2). Did I say the battle is vast? On one day last week, there were 342,418,226,849,748,675,496,726 of these little guys roaming my aquarium, looking for action. Some of these are paratroopers, arriving at the aquarium out of the air. Others are made in secret labs, otherwise known as photosynthetic organisms such as many corals and algae.

Unfortunately, despite their vast numbers, the oxygen molecules are not very effective fighters. In many cases, they can swarm all over the enemy and still not prevail. The true leaders of the oxidizers are far less numerous, but considerably more potent fighters. These include ozone (O3), hydrogen peroxide (H2O2), triplet oxygen (3O2), and a variety of oxygen radicals, some with such inspiring names such as superoxide radical (O2-). They also include chlorine (Cl2) and chloramine (NH2Cl). It turns out that oxygen molecules (O2) can occasionally morph into some of these better fighters (such as hydrogen peroxide), sometimes all on their own, but most frequently when they get blasted with UV light.

The oxidizers also have other types of fighters. Some are present at very low concentration, but are so sensitive to the state of the battle, that one can gauge the battle by how many of them are left standing at any given point in time. Metals, for example, such as iron (as ferric ion, Fe+++) can serve this purpose. The other oxidizers also include anions such as hypochlorite (ClO-), iodate (IO3-) and nitrate (NO3-), among a host of others.

On the other side are the reducers. The reducers all want to get rid of electrons, and they virtually throw them at the oxidizers. Many of these are organic molecules. They are not as numerous as the oxidizers, but many are much larger. Some are more than 10,000 times as large as an oxygen molecule. So they can make up for low numbers with pure brawn. That is not to say that the reducers do not have small but potent soldiers. The antioxidant vitamins, like vitamin C, for example, are small but extremely potent reducing agents. The reducers also number on their side some inorganic compounds, such as ammonia, iodide, and a really nasty fellow, sulfide.

The reducers come from fish food, metabolic waste products, the breakdown of dead organisms, and certain additives put into the aquarium (e.g., iron supplements that contain ferrous ion). The surfaces of most organisms themselves enter the fray as reducers, waiting to be oxidized by the enemy.

Interestingly, most soldiers on both sides are suicide attackers. Oxygen, ozone, and hydrogen peroxide are all destroyed when they react with a reducer. While not strictly suicidal, most organics are heavily damaged by oxidizer attacks, and are slowly degraded, eventually ending up as carbon dioxide if oxidized enough. They tend to be found in areas that the oxidizers hate; that is, in areas of low oxygen. Yet, the reducers are also sneaky, and even manage to get their hands inside cells (even finding positions in photosynthesis itself).

 

[zoomonster]

Howdy R2R! Question for the more knowledgeable folks out there...

I have a system that I frankly haven't paid much attention to over the last couple of weeks, ORP reading 425, stopped ozone on that system a month ago because it was making my skimmer go nuts. I was running ozone through a Reef Octopus reactor, ozotech with luft pump, but like I said, I haven't run that for a month. When I was running it, couldn't get ORP above 325, but now it's been rising since I turned off the O3... I also have biopellets running and have a Avast Marine purigen reactor that runs all the time. The probe is clean and I am pretty sure it is accurate.

What would cause my ORP to get this high? I know it's *probably* a good thing, but want to understand the chemistry behind it.

Thanks,

Lloyd

I would have to think your ORP probe is screwed up or fouled. I'm running an almost identical setup (Ozotech, RO XP3000) and use ozone to keep ORP in 370-385 range via Apex and it runs smooth. Never had an issue with skimmer going crazy from ozone use. Now when this tank was new and I had been using Bacter-gen from continuum aquatics I finally figured out that bio film from the product was continually fouling the ORP probe and that resulted in ORP readings going high such that ozone would never come on. Every few days I was having to soak the probe in vinegar to get it working again. Now its sensitive enough that all it takes is a tank feeding to kick ozone on. I don't even remember when the last time was I had to clean the probe.

Of course I don't run biopellets and not sure what effect that purigen reactor has. I suppose either could be fouling the probe. As far as skimmer going crazy don't think thats from ozone. Usually its something you are adding to your tank.

 

[nervousmonkey]

Thanks Randy and Zoo. I've read that ORP article many times actually, great article! ORP is definitely not a concept that is easily defined... After reading both of your responses, I thought back to the last cleaning, a couple of weeks ago after I stopped the ozone, and it hit me that something must be fouling my probe, so I took a Q-Tip to it and it dropped immediately to 377, so then I just took it out and started cleaning it with vinegar.
What's strange to me about ORP though, is that I took a lot of chemistry at GaTech, 3 years of inorganic, organic, physical and another year of biochem, so chemistry is not a stranger to me conceptually, but ORP is... I am no Randy with a PhD in chemistry, and only say that as a background to understanding ORP, but that one gets me. I'll have to study it more!!
Funny Zoo, I hadn't thought about that before, but I was adding Pohl's to the tank along with the ozone, so that's probably what set my skimmer off, just thought it was ozone.
Man, great to get other people's opinions. Funny how something simple like a bad probe can make me question everything about my set up... Thanks again guys!