Brenmuk said:
ceg4048 said:
The fundamental reason for doing a water change is to clean the tank of toxic substances produced by the accelerated metabolism of plants due to their uptake of CO2 and nutrients. These waste products are not only toxic, but they encourage algae as they biodegrade. Not cleaning an EI tank encourages algae due to the excess dirt and organic waste. It also encourages poor fish health. The fact that changing the water also "resets" the nutrient levels is merely a coincidence some find convenient.
Cheers,
ceg4048
Out of interest what are the toxic substances released by plants? I might be wrong but I seem to remember you arguing that the reason for water changes was to dilute algal spores?
Hi Bremuk,
While getting rid of spores is one of the arguments, it isn't a primary one for a stable tank. Multiple water changes that delete spores is one of the techniques used when one is addressing an algal bloom. Vegetative algae produce spores in abundance, which then bloom and produce more spores. If the tank is suffering a bloom then that means the trigger mechanism has been activated so that needs to be addressed. Clearing the tank of as many spores as possible helps reduce the quantity and severity of the bloom. Under normal, stable conditions we don't really pay too much attention to the level of spores because it's relatively low anyway and as long as they stay as spores it's not a big deal.
The proteins, amino acids, fats and carbohydrates that are expelled from the plants during accelerated metabolism become problematic in the confines of the tank. They become part of the biofilm and block access to nutrients/CO2. These products also decay, lowering the oxygen content which have an impact on fauna. The ammonia loading rate is affected in the decay process and the spores of some algal species use this rate as a trigger mechanism. People don't realize how important it is to have a clean tank. When a tank is being setup, there is
not enough of these products and so the tank becomes unstable, which triggers algae. When the tank is mature then we have
too much of these products which can trigger algae. So yes, absolutely we want to get spores out of the tank with water changes, but fundamentally we want to use the water change to clean the gunk off the surface of the plants, clean the water column of organic pollution and to unload the sediment of built up debris and detritus. People are so freaked out about nutrients that they miss the boat entirely. In a fuel injected tank, keeping it meticulously clean will be the best possible thing you can do for plants and fish.
While the microbes that perform nitrification do appreciate the products expelled from the plant, the buildup is too much for the plants and animals themselves. With non-CO2 / lean dosing programs, since the nutrient uptake is much slower, the expulsion rate of organic waste is also much slower. The plants adapt to the low nutrient/CO2 rate, become leaner and much more efficient, reducing the waste expulsion even further. It's a much more stable approach as long as the lighting level is not excessive. Enriching CO2 automatically sends the tank into the passing lane of The Autobahn.
Stickleback said:
In that case, supposing you were keeping to the low tech dosing regime, they would then become nutrient limited. You would therefore expect to see algae?
As Andy notes, since carbon enrichment defines low tech/high tech then a low tech tank is basically CO2 limited. The CO2 limiting occurs faster than NPK limiting, but even low tech tanks can suffer NPK limiting. But this is easy to fix with fish in the tank. Adding small amounts of inorganic salts, either to water column (weekly or bi-weekly) or to the sediment allows faster uptake and better health. Healthy plants will resist algal attacks, so no, one does not necessarily "expect" to see algae in a low tech environment.
Cheers,