There was another thread on here about spring clean outs and it got me thinking about a related subject. When a new pond/water garden is installed, we all know that it takes a certain time period for the biological component of the filtration system to get up and running. So we let the system run, maybe add some bacteria or even water from another healthy well balanced pond and wait patiently until adding goldfish or koi. Once the filtration system can safely handle a fish load, then fish are gradually introduced. Now if we accept this as standard practice and the "correct" way of doing things, let me pose this question: How does a spring cleaning service that entails a total drain, pressure washing, scrubdown and refilling with fresh tap water differ from a pond that was just built? In the case of the spring cleaning job, we house the fish temporarily while we do the cleaning work and then put them back in the pond when we are done. Let me be clear here that I am not making any judgements on how each contractor works or the methods he follows. I am more interested in starting a discussion about whether or not we can improve our methods and make them more consistent from start (install) to finish (recurring maintenance). So how can we tell a customer that they must wait a set time period before adding fish when the pond was new but it is perfectly fine to drain and refill their pond in spring and chuck the fish back in right away? Perhaps this discussion is more relevant to those of us that work in cold weather climates that require the dreaded "drain & dump" cleaning technique. Again, without getting sidetracked and moving this thread into the realm of what is right and wrong with installations being done, I just want to talk about what is the best way to handle the jobs that have already been installed. So if a pond requires a total drain, cleaning and restart then how can we explain/justify/support the notion that the fish can be put back in immediately? Are we off track on the need for an initial start up period? Do we believe that starter bacteria and other additives make the pond safe right from the start? Maybe we hope that enough dormant bacteria survived the winter and the thorough spring cleaning process and it will quickly activate and make the pond safe for fish? This then leads me to another question. Is there a difference between a drain/clean situation and a pond that goes through winter (again assuming a cold weather climate) and experiences a period of dormancy in which the bacteria are performing little or no bio filtration? Will the fish experience a different set of stressors in a dormant pond waking up and starting anew in the spring as compared to the same pond being drained and cleaned and started back up with fresh tap? What role does bio film and anaerobic (working on the assumption that most of the aerobic bacteria was dormant) bacteria play in making the undisturbed pond better or worse for the fish during the spring "wake up" period? I would like to hear everyone's thoughts and opinions on this subject. And for those guys that work in warmer climates where this problem may not exist, is there some other cleaning related issue you have to deal with that doesn't affect us cold weather guys?