Hi, a question came to mind the other day as I was continuing to incorporate an ecterior bog filter to my waterfall. I have a small backyard pond. Its around 12' by 7' by 36" deep. I made my own biofilter using a 5 gallin square bucket to which also acts as my waterfall weir and its been working fine. I recently decided to create a bog filter utilizing a 150 gallon stock tank that i will incorporate behind the existing waterfall allowing me to expand it and thus eliminating the current 5 gallon bio filter. I left enough liner when i first built it cause i knew someday Id want to make my waterfall bigger. So...when complete, the 3500 gph pump which is placed in the middle of the pond, will pump water into this 150 gallon tank which is now a bog filter and will flow out creating my waterfall flowing back into the pond. Now....my question...during the initial startup of this bog filter, the pump will remove 150 gallons from my pond and fill the bog before flowing back into the pond. And I assume this will cause my pond to significantlly lower the water level. Will the absence of the established bio filter cause a shock to the pond since im eliminating the bacteria that was in the bio filter? I mean the new bog filter has no bacteria in it yet ad its brand new. Will this cause my fish to go into shock?and what happens when i replenish the water when i bring it back up to level? Wont this disturb the chemistry?