sort of depends; if you leave your preform empty for too long, the good stuff is going to die and you'll be starting all over again with NPS (new pond syndrome).
This is going to stress both you and the fish, so monitor and don't over feed. Depending on where you live, i.e. temps, if the fish are going dormant for winter, no problem not feeding. If you're in an area where the fish are still active, the NPS is going to hit. IF you can, strain/sieve the water you saved before you put it back but the good stuff was on the walls, NOT in the water, so fresh water will be fine except you have to worry about matching the pH, adding any dechlor, and temp should be within 5 degrees with any acclimatization being a SLOW process so the fish can get adjusted. In the future, plan on working fast i.e. taking out the water, cleaning the bottof of any guck, putting the water back in and then the fish. This way, you minimize workload AND stress on the both of you.
If you have bog, it'll help; if reg mech filters, hopefully the pads did not dry off and you have some good bacteria there. Your dark green water WON'T be clear by filtering (single cell algae is too small to get out by conventional pads/filters) so you're going to have some no matter what but that free floating algae may be saving your fish as it's THEY who are eating the excess DOCs in your pond. That amount of floating green means you need more bio filtering and lots of plants!
Good Luck!
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