Join Date: Feb 2019
Location: United States Oregon,
I measure ORP using an Apex
Yes have been measuring Oxegen Redox Potential (ORP) since I started my tank over 3 years ago. Like you I went nuts reading up on it. Above are some good articles if you want to dig in. I would not go there unless you are a chemist. There are a couple of simple things to understand about it. First it is measuring the waters ability to reduce oxidizers. Oxygen is involved in most oxidative reactions but ORP is not a measure of oxegen. Similar to pH it is measuring + and - ions but in reverse of the pH scale. Regardless of the details, like pH, too much acid or too much base can burn mucous membranes and kill so we keep our tanks at around one pH point from Neutral depending on the native habitat of the fish we keep. Too many oxidizers or too many reducers can burn mucus membranes and kill.
Again like with pH it is important to know what is normal when reading ORP. Is the fish from a lake, pond, slow moving stream or fast moving stream? Most fish live in waters that are in the range of 400 to 450. If you use CO2 you are going to see the pH drop and the ORP go up over the course of the day. This is normal and I control my CO2 with a combination of ORP and pH. You might say I control my pH and my ORP with CO2. I have South American Cichlids so I have a target pH of 6.8 and a target ORP of 450. If either the ORP gets to 490 or the PH gets to 6.5 the CO2 shuts off. If the pH goes over 7.3 I get an email alert but this has not happened yet since I use ground coral and Wonder shells in the tank as kind of a buffer. ORP drooping below 400 also sends me an alert.
Adding too much fertilizer can raise hell with ORP so this is the main point for me to even look at it. I am saying these things in the least technical way so you tech heads out there do not pick on me.
One last thing which is probably the most important thing about looking at ORP. Probes like the ones that come with the Apex get dirty over time causing the ORP READING to slowly increase. If I see a rise in the ORP reading the first thing I do is take the probe out and clean it with a toothbrush to see if the ORP drops back to normal. Thus far it always has. Be careful when cleaning as the glass bulb is very fragile. Most important thing to clean is the small white membranes. Please do not get lost in the complexity of the articles on ORP and simply use it as a way to know what is normal in the tank. Oh and there is no way to accurately calibrate an Apex ORP probe. If it fails to correct after cleaning or acid soaking like they recommend then get a new one. Life is too short to mess with bad equipment.