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ORP and carbon/GFO reactor

Dan H

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So I was checking out all the apex logs and noticed an interesting trend... Last Saturday around 3pm I changed out the carbon and GFO in my reactor. The reactor runs for a total of 6 hours a day, in 1 hour runs. I noticed that when the reactor is on, the ORP in the tank comes down a bit. Nothing dramatic, but certainly noticeable.

But here's the cool part, it seems that fresh media seems to affect the water much more than the old stuff. Prior to switching it out the media was approaching 2-3 weeks old. When it would be on, there was little swing in ORP. As soon as it was changed out, the ORP would swing much more. You can see the little increases in amperage along with a slight drop in ORP. Obviously many other things affect ORP so it's all over the place, but there sure seems to be a pretty good correlation here. Also, it's hard to say if it's because the media was packed in as it aged, or if it was used up. I'm guessing both. After 2+ weeks it seems like the carbon and particularly the GFO gets packed in and stops allowing as much flow through the reactor.

Check out these logs:


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I have a couple of thoughts here:

1) It *might* just be related to electrical interference from things kicking on/off (you sometimes see dips when the heater kicks on), how close is the ORP probe line to anything which could cause line interference?

2) I don't think that the carbon would be affecting GFO directly, but perhaps as it removes organic matter from the water, it should be increasing the ORP by proxy as a result of a reduction organic matter which typically depresses ORP. However, that is the opposite of what your chart shows (ORP dips when reactors kick on).

3) I've gone round and round on this, because ORP is a ***** of a parameter, but I cant reason out why GFO would have a direct affect on ORP. It's not an open reaction of GFO & Tank water, as the Phosphate is binding to the Fe3+, which should keep the whole thing relatively neutral in terms of imbalanced charge. There are just a ton of parameters that affect ORP, and it's hard to suss out what is truly the causative agent here. You have to contend with variability in pH, dissolved oxygen, phosphate, flow rates in the reactor, etc.

By far the biggest modulator of ORP in reef tanks (assuming one is not running ozone) is going to be pH. Those pesky hydronium ions (i.e., an increase in H+ ions (H30+) or a reduction in pH) have a secondary oxidizing catalytic effect whereby other things are more effective oxidizers (increasing ORP).

You could test all these theories by taking one or both reactors offline for a day, but continuing to run the pump.

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I like that experiment idea. I may just try pulling out the GFO for a week, then pulling out the carbon for a week, and then try it with none. See if it still has the same pattern. Well, once the current GFO/Carbon is used up, I may just do that.

The pump that runs the reactor is about 1.5-2 feet away from the probes. It's possible it's interference, but none of the other probes - including conductivity which is really sensitive to interference - seem to be reacting to the pump.

Another theory I just thought up is that when the reactor is off, the water in the reactor may become stale and hypoxic since it's just sitting there. Then the pump kicks on, pushes out all this "bad" water which then causes a quick burst of lowered ORP. hmm.png

Another thing I can do to confirm it's the reactor is run it for 2-3 hours bursts instead of 1. See if the ORP behaves the same pattern.

And yes, ORP really isn't all that useful, but I did find it to be interesting data. I just like data.dribble.gif

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Bunch of nerds in this thread. It's a little late for me to add input but I was thinking stagnant water myself. Also a reason I wouldn't recommend shutting off/on reactors like that.

Other reason being the GFO has a tendency to condense into a giant ball and not tumble as well.

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I'm definitely going to play with this and see what the data says.

Ironically Ty, I used to run the reactor 24/7, but then I found that it actually clogged much faster if when it ran non stop. After 1 week, the GFO was a brick. Now that I'm "pulsing" it, it will stay fluid for 2-3+ weeks. Granted that could be a function of less phosphate to absorb, so it's not binding up as much... But meh... Seems to be working for me.

The only other change which may or may not have any affect, I moved the reactor out of the sump (as in literally in the water) and mounted it to the wall of the stand. It could get warmed up while the pump is not running (the inside of the stand is usually about 83F. Not sure if that has any affect but possible.

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Ugh, ORP! I can't tell you how much I hate looking at ORP when waiting for it to stabilize in the field collecting ground water samples. It's insane how quickly ORP can change from different variables. I can see why some people would want to monitor it, but I don't think I would ever bother. There are some pretty intriguing ideas coming from this thread right now though, I do enjoy contemplating the cause.... But the important thing is what's the effect in the tank?

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