The AG logo in the middle of the grow plate pops up. If you just lift it up with the pump turned on, you'll be squirting all over the place. Stop the pump, stick the drain tube in it, turn the pump back on. Takes a while, but I'd usually start one side up using the built-in pump while I drained the other side using a battery operated siphon.
Dig around in the menus to get to the drain wizard. I think maybe the little pump logo on the front display is also a shortcut to the wizard.
The uncovered fill hole is one design aspect of the Farms that had me scratching my head because I was worried about exactly this. I’d try the peroxide Dawn mentioned once you refill. Just don’t put too much in like I did which killed off some of my gardens.
Well, I dumped and refilled. I couldn't get it to drain, though. After further reflection, I'm not sure I like that feature. A separate electric siphon is a better option. The biggest question, for me, was why it occurred.
It did not happen with the AG Ghost peppers in the left bowl. They both had the same water source. They were both washed with a Dawn soap water bath to remove any manufacturing chemicals. The only differences are the seeds and the sponges. The unaffected side (left) are AG Ghost pepper seeds and sponges. The side with algae (right) has Burpee organic Red Habanero seeds in Park Seed sponges. I have never had problems with Park Seed sponges.
But this occurred so quickly, within two weeks from planting. That is what really puzzles me. I washed and sterilized the bowls.
FYI: Taking apart this grow deck is a real BEAST compared to the Bounty. There is a thick lip that makes it really difficult to get something underneath to prevent it from snapping back together..
I did not use Hydrogen Peroxide, this time. Most of the algae was in the bottom of the fill hole. Some more was at the top of the water level on the left side of the bowl. And I got some out of the pump filter, too. I'll have to keep a close eye on that bowl.