Fish excrement is rather the smaller problem. The NaturaGart filtration technology reliably removes these particles from the water.
Fish feed contains a lot of protein and this in turn a lot of nitrogen. Humans excrete nitrogen with their urine. In fish, the gills take over the function of kidneys: Not only do they absorb oxygen, they give off ammonia to the water. This only works, however, if there is no ammonia in the water. Below a pH of 7 this is never the case and fish don't have a problem.
Above pH 7 ammonium in the water changes into ammonia. Up to pH 7.5 most fish can handle this fairly well. Above this value the situation escalates: Fish get the same problems as humans with complete kidney failure. Nitrogen compounds invade the body and poison so many cells in few days that death becomes inevitable.
In stable systems this situation is avoided because underwater plants use the ammonium as fertiliser and bind it. The levels of ammonium are so low that hardly any ammonia forms even at high pH levels.
Where plants are done away with, problems are bound to happen. The concentration of ammonia rise and high pH levels create a risk of poisoning.
Independently of the direct transformation in plants there is another way to reduce ammonium concentrations. Given enough oxygen, certain bacteria can transform ammonium into nitrite. This is even more poisonous than ammonium but in a further step other bacteria transform it into largely non-toxic nitrate.
Practically all biology textbooks picture this as a perfectly tuned procedure. With sufficient oxygen, neither ammonium nor nitrite should be detectable. Reality is more complex than that, though: Even with in mostly oxygen saturated water and using somewhat more involved analytic methods, we always found all decomposition products together. In our opinion, the only way to completely solve the problem is with underwater plants.
All solutions that do not use plants merely postpone the problem. Even if you manage to mostly oxidise ammonium and nitrite: Nitrate remains in the system and is only diluted by changing the water or used up by algae.
The filtration system takes care of the latter and thus exports nitrogen out of the system.
In inefficient installations there will always be a slight haze of algae that absorb the nitrogen compounds. The NaturaGart system, in conjunction with UV, clean water so effectively that hardly any algae exist to take care of nitrogen export. This is always an extreme situation when small volumes of water are pumped through the filters 10-20 times per day. That will eliminate 100% of algae. We therefore recommend to combine such extremely filtered ponds with a plant basin.
