Apex ORP it's just a number question

[Homer Allman]

This question isn't about what it is or what it does. It's simple question. What numbers are considered good and what numbers are considered bad when using the ORP probe? What does high numbers tell you and what do lower numbers tell you.

 

[trido]

Orp numbers are all subjective. The higher the number the cleaner the water. In theory..... Orp probes in our hobby are inaccurate at best but great for trending.
For example, I have an SPS dominant tank, run filter socks 24/7, run carbon, have and algea scrubber, also have a chaeto reactor, use ozone and do WC's every other week. My Orp probe reads from 280-320 depending on the month.
A friend has An LPS softie tank and dont do WC's except when things are looking poorly, doesnt do much of anything except let Darwin run the tank. His Orp reads 460.
I have a very hard time believing that his water is cleaner than mine. If you dont like your Orp reading, try cleaning the probe, it will likely change, buying a new probe will also give you different #s. Calibrating your probe to get an accurate number is the only way to really know the reading but it isnt necessary for our purposes. Its great for trending. When I run ozone for long periods of time, my number rises, when I feed I can see the number drop immediately. When my numbers drops over a weeks time, its a good reminder that I need to change my carbon. But, my reading of 260 is irrelevant to the friends reading of 460.

 

[Homer Allman]

Thank you for answering. My tank sounds like your friends tank. My numbers are always in the mid 400's. My nitrates and phosphates and sky high. I have 300 gallons of water in my system. I am trying the confirm which way my numbers should go if I do more water maintenance. I did a 10% change yesterday and the ORP numbers went down. to 389

 

[chipmunkofdoom2]

Many people tend to describe ORP as a measurement of "cleanliness" of tank water, but that's an oversimplification. I don't think it needs to get a whole lot more complicated, but it should be a bit more thoroughly explained as cleanliness is not actually what ORP is. The article by Randy Holmes-Farley summarizes ORP best. Here are the most relevant bits:

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.

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)

On the other side are the reducers. The reducers all want to get rid of electrons, and they virtually throw them at the oxidizers. 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)

Is ORP a useful measure? That is, should aquarists really care how this incredible battle is going? To some extent, yes. If the oxidizers carry the day, the ORP would rise to the point where the organic molecules that represent the bodies of organisms would be burned away. If the reducers won outright, the ORP would drop below 0 mv. In that case, there would be little oxygen left, and toxic hydrogen sulfide would rule the aquarium. In either case, the aquarium would be a disaster.

So aquarists have to hope for, and to some extent maintain, this battle in a sort of middle ground. That middle ground is typically described as being between 200 and 500 mv. Most aquarium authors have recommended a range of 300-450 mV. Why? Mostly because the ocean often has ORP in this range, and because these authors have successfully operated aquaria in this range.

 

[Homer Allman]

thank you. that was deep!

 

[ca1ore]

While I accept the conceptual 'argument', in any sort of practical way I have found ORP useless. I've measured it for decades, back when I used ozone. Since then there has not been a single time where I took some action as a result of an ORP measurement - well, other than running around in a 'panic' trying to figure out why the reading dropped by 100 points in an hour. Almost never figure out why LOL.

 

[lapin]

Just because inquiring minds want to know.
So I got a orp probe cause the apex has a place for it. Looks like it is around 180 in the afternoon and about 220 in the middle of the night. Is the swing a normal swing? More junk grows (organics them be called ) with light on in day perhaps? Goes up after a water change which I expected. I really dont care about chasing any number, I just want to see what my tank was at. For $75.00 I got my answer.