I’ve often heard, and have said myself, that you can’t have too much filtration. I believed that. However, the size of your filter is as important as the pump and flow rate. As with the pump, if it pumps too hard the water will not have sufficient contact time inside your filter. If it pumps more slowly, it may allow particulate matter to settle to the bottom of the pond, rather than be carried to the filter as it should be. Too small a pump can also result in “dead” pockets with poor circulation. You may even have to clean it out a couple of times a day to keep it running right.
Everybody wants a biological filter, right? At least “part” of the filter should be biological activity, even if the rest is mechanical. What is often overlooked is the food to mass (F/M) ratio. If the filter is undersized, the bacteria will tend to produce more polysaccharides and stick up the mechanisms. If the filter is over-sized, something entirely different occurs; there is not enough food for the bacteria to multiply and fill up a too-large filter. And with that there will be no opportunity for the bacteria to denitrify. De-Nitrification HAS to occur in anoxic zones, preferably in the bio-film in your filter. So, if year after year you continue to struggle with pea soup and other types of algae, you may want to look at your filter size. So, now you can see why oversized filters can present as much of a problem, in the long run, as undersized. My suggestion is to buy your filter according to the amount of fish you are keeping rather than the volume of water. If the bio-mass (food source for bacteria) has increased, whereas your pond used to look great but no longer stays clear, it may be time to upgrade to the next size filter.
I had problems with my pond clarity in the second year. I couldn’t figure it out. I was keeping only a handful of koi in 4,500 gallons of water. I had a huge bubble-bead filter, pressurized prefilter mechanism, and Bakki shower… the works! I had a 1.7 HP motor. Whatever could be the problem?? In my case, it was too much filtration and too few fish. The solution? I downgraded the pump to 1/3 HP, increased the fish load and if that doesn’t solve the problem, will downgrade the filter as well. Because I need the bacteria to not get lost in there…I use MICROBE-LIFT/PL and I know they can and will take the nitrates out, if I give them the chance.
PS-
When I removed the Bakki shower and the pressurized pre-filter (talking about MY CASE HERE) and lowered the pump to 50 GPH, the results were automatic! And amazing! No more algae and no more spring “green water” or other problems with the water quality.
