Understanding ORP & SPS Colour
I was recently asked a question on Oxidation Reduction Potential (ORP), why only "some" marine enthusiasts utilise this specific parameter testing in their daily/weekly water analysis and how it can effect colour within SPS corals. Having a background in water treatment and nutrient control, I was also curious to understand specifically how this seemingly overlooked measurement could help in the
"reefers" world. Many articles you find on ORP can be comprehensive and somewhat in-depth for the average reefing enthusiast. I started writing this article to "simplify" ORP and share how I interpret it. ORP, in simple terms, is the measurement of volume of oxidisers in the water in relation to the volume of organic molecules. Oxidisers being 02 (oxygen) and 03 (ozone/oxygen radicles i.e H2O2, 302, etc). Oxidisers are also extremely unstable electrons, they are hungry and aggressive and therefore force the breakdown of organics and dead organisms.
The higher the oxidiser volume, the higher the breakdown which in turn leads to cleaner water. ORP measures this in millivolts (mv). The higher the ORP, the higher the chance of oxidation. It is not a direct indicator of bacteria count, more so the quality of water within the system. This means the higher the ORP, the cleaner the water. For example, if you are not utilising ozone and you are running a healthy ORP then your system has established a high bacteria count compensating for any organic build up.
Now let's talk about ozone. Most ozone kits run off a controller programmed with a high and low value ORP, typically running between 375mv and 400mv. Understanding biological and chemical breakdown (ozone) will give you a comprehension of ORP on both oxidation scenarios. This is where ORP can be extremely valuable. From my domestic and commercial experience both at home and in large scale aqua-cultured farms, I have found the "most desirable" ORP levels to be between 300mv and 400mv. Exceeding 480mv will inevitably start to kill tank inhabitants and over 650mv will kill most bacteria in seconds.
Reading up on ORP and understanding its possible foreseeable applications makes me really wonder why this is not an essential/vital piece of equipment for the average reefer. To anticipate a tank crash, a considerable drop in water quality/clarity is priceless let alone having some source of control on a biological scale.
Having the knowledge to understand how ORP levels influence tank inhabitants through the measurement of water quality/clarity, will allow you to appreciate how SPS corals are directly effected. Acropora Valida is perfect example. Even the advanced enthusiast struggle to achieve the intense rich purple luminosity this coral presents making it one of the hardest to keep in its true colour. Understanding ORP and water clarity may reward future reefers to perpetuate such true standards.
If you want to learn more about ORP, here are a few links for further reading which I have found to be useful:
Until next time happy reefing!
Reef Anabolics