Originally Posted by pop
I don’t understand the need for two filters if one is all you need. Why would several filters not running at capacity or top efficiency be better? The filters might compete with each other for bacteria reducing the biological efficiency and creating ecology for bad bacteria to reside as well as reduced mechanical efficiency in both filters.
Are the currently developed filters so poorly designed that a back up is necessary fore the predicted failure of the fist filter.
There are a number of reasons why I prefer having two canisters instead of one. I wish I could explain why, but I don't discuss such matters on the open forum.... not since the powers that be told me my views and methods are wrong. In fact I've broken my own rule about abstaining from offering filtration advice just by posting in this thread. However, I like you so I am making an exception.
I don't think it's good for filters to run at full capacity - doesn't leave any room for growth. I like knowing that I have plenty of room for bacteria to live, so that as the fish grow, I don't have to worry. I also like knowing that I can stock anything I want in the tank and not have to worry.
I experience increased mechanical efficiency with two filters, not decreased. In my systems, there is twice as much mechanical media as there otherwise would be, so it takes twice as long for the filters to get clogged. There are also multiple pickup points versus just one. I don't see how running just one filter is any more efficient than running two, but I can see a number of ways that it's less efficient. I don't have any issues with "bad bacteria". The bioload of the tank is split between the filters, so yes I suppose they do compete with each other in a sense. Competition is generally considered a good thing. I like the idea of one filter trying to process more ammonia than the other, or collect more waste than the other. I fail to see how expanding the overall capacity of the filtration system could have a negative impact on the biological efficiency.
HOB filters are prone to failure by design. The motor is at the bottom of the filter, where things settle. Too, the water that runs through the motor has not yet been filtered. Most people that use an HOB on a sand tank will agree that the potential for filter failure is quite real. Canisters, on the other hand, have their motors on the top of the filter. The water that runs through the motor has run through the various stages of filtration, so the potential for an obstruction of the impeller is quite low. Canisters are impervious to sand, for that reason. That all being said, I don't run 2 canisters on my tanks because I am concerned about one failing. It is an added bonus, though it did not play a role in the decision process. Personally, I feel that there is ample time to fix the problem in the event of a filter failure before there is a problem in the tank, and my own experience with power outages support that.