using ORP probe to determine if water change is needed.

[sammie]

I have recently been trying to monitor my ORP via probe and apex controller to determine if a water change is needed and I noticed something unusual. I have my ATO hooked up to a kalk reactor and everyting the ATO kicks on and tops off the tank with kalk water, the PH rises slightly, which I would expect and the ORP reading takes a nosedive. Is this normal? I don't run ozone just using the ORP probe to get a reading. It usually runs between 325 and 425. I also noticed the ORP drops when I do a water change which I would think it would go up.

The system is a 300 gal DT, 2- 65 gal frag tanks and a 85 gal sump with all the goodies. Growing an assortment of LPS and SPS with a few softies in for effect. I change 60 gal of water weekly with all parameters in line with NSW.

Anyone else try this or can a ORP probe not be used to predict needed water change?

[tmz]

Orp is complex , I monitor it just because I have a monitor. It can't predict a waterchange need, ime. This article may be of interest:


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

[sammie]

Thanks for the article, very interesting but it poses more questions than answers. He discusses some of the things I've noticed that effect ORP and the relationship between pH and ORP.

[bertoni]

An ORP probe might give you some idea of the organic content of the water, which can signal the need for a water change, but it won't detect the buildup or depletion of trace elements and other ions in the water, so it only tells part of the story.

[sammie]

That is basicly what I was thinking, to determine when the organics are at a certain level and need to be removed by a water change. The above article by Randy shows that it's much more complex than just organics and I think I'm seeing the same thing as I monitor ORP. For example you would think the OPR reading would go up after a water change if the level of organics are reduced but I'm not always seeing that.

[bertoni]

The ORP level often seems to drop with water changes. We've never determined why. That'd be complicated and expensive, most likely. You could test the ORP of the new water before adding it.

[tmz]

A lot of interactions occurring in the blink of an eye make it hard to understand what you may see at any moment.
For example some who dose hydrogen peroxide don't see a rise at least not immediately; but a drop ;maybe the oxidation is just too quick to see and newly degrading refractory organics show up .
Removing higher nutrient water during a water cahnge may also be removing nitrate ,an oxidizer, and other oxidizers. outweighing any reducer removal.

Generally, I watch it for changes which may indicate something is going on in the aquarium but then I have to check other things and deduce what change might have occurred and whether any intervention is needed.