Have a slightly different take on filtration, nitrates removal and other ills from accumulated fish poo is handled.
Mine is an in-pond biological filter and instead of bio balls, bio rings etc, its merely a 30cm thick layer of granite chips, yes, they type used in construction. To keep the bacteria alive, underground pipes blow water through and upwards. As well, my pond is laden with around 20 different types of water plants, which in turn remove all the nitrates that the bacteria does not/cannot consume. So, apart from having the fun of having all the different water plants, the overall feel is an amazon river where even sensitive Altum angles thrive with nary one death in a batch of 10 i intorduced about 10 months ago.
While i have just 12 rays of different sizes ranging from 15 cm to 60cm diameter, have over 30 types of monster fishes in the same pond of around 40,000 litres.
Backtracking a little, biological filter covers half the pond surface.
In essence, i am far less scientific when it comes to filtration construction and rely on plants and natural bacteria to do the job. Even all the roof top gutter is planned such that it flows into my pond and by default, i get a massive water change evertime there is a downpour. I will be the first to admit that PH swings should be incredible, but for whatever reasons, it has always been around 6.5 and the variety of fishes all seem to have adapted.
Not sure if my "natural" system have mangled your ideas of how to make a better filter system, but consider using water plants in abundance if your setup allows.
BTW, you have one heck of a collection of rays, be it quality or quantity!
Regards
Boon
