Hi all,
ORP measurements seem prevalent with reef keepers but there was a suggestion that it was equally useful for freshwater.
We have a couple of threads that mention <"
ORP or REDOX"> values.
If you look at the situations where people are most interested in them (Reef Tanks, and to a lesser degree Rift Lake Cichlid keepers), it is in alkaline, highly oxidising environments where the higher the ORP values are the better. It is a "
black and white" scenario where high ORP values are good, and low ones are bad.
If you think about <"
foam fractionaters or protein scrubbers"> they are physically removing DOC from the water, but you can use chemical options, and I think some shrimp keepers use the <
"Söchting Oxydator">, a hydrogen peroxide (H2O2) generator. A substance like Purigen (and the Twinstar Mini/Nano) probably fits in here somewhere as well.
I guess the question I have is whether redox is actually important? This is a proxy for BOD so presumably it would be an indication of a build of of organic waste or overstocking?
It is, but we are back to the "shades of grey" argument.
If you think about a Coral Reef (or the surge zone of Lake Tanganyika), it is a very small specialized part of <"
a much larger ecosystem">. In the case of the reef, its survival might depend on the Turtle Grass (
Thalassia testudinum) meadows in the lagoon, fringing Mangrove swamps behind the lagoon and the huge volume of nutrient poor ("oligotrophic") open ocean washing over the reef twice a day.
These areas are performing many of the other functions that produce the stable, low nutrient, low sediment, highly oxygenated conditions that the reef needs. You don't have the luxury of a <"
mangrove swamp"> etc. in a normal reef tank, so you have to use other means (deep sand bed, protein skimmer, phosphate/calcium reactor etc.) to retain water quality.
I like to think of ecosystems as spatial and temporal mosaics, patterns in space and time, that replicate themselves on <"
different scales">. If you think about freshwater streams and ponds etc the situation is slightly different, you don't the same spatial separation of the different functions, but they are still occurring. You also have much more terrestrial input of nutrients, dead leaves, sediments etc.
In a planted freshwater aquarium we help nitrification along by providing a biological filter (which allows us to keep more fish), but other than that we can replicate the natural situation more closely.
In a tank, with a substrate and plants, you will have different REDOX values:
- in the deep sediment there will be reducing conditions (negative REDOX potentials)
- and in the rhizosphere/upper sediment (zones with diurnal REDOX negative/positive fluctuation)
- and in the tank water (always positive).
The zones of negative and fluctuating REDOX values will be particularly important in making mineral nutrients available to aquatic plants. The natural REDOX values of streams and ponds will also vary and they would be much higher in a chalk stream (or Lake Tanganyika) than in a black-water peat swamp.
The only place where I explicitly like a spatial separation between the aerobic and anaerobic processes is in a canister filter, the reason for this is that you have a finite amount of oxygen that enters the canister and you run the risk of ammonia rich, de-oxygenated water, flowing back into the aquarium.
This is back to <"
risk management">, even limited exposure to low oxygen and/or high ammonia is going to kill your fish.
cheers Darrel