I am on my third hempy grow -- old gatorade bottle cut in half. For some reason, this time around, I am getting some green sludge on top of the perlite. I have 4 layers of duct-tape around the bottle, but nothing on top. I am pretty sure having something covering the top would have prevented this.
Any way to remedy this? Should I be worried? I read that DWC growers use a little hydrogen peroxide to clear this up. Is that advisable with the hempy style?
And advice appreciated.
Yeah its just algae, and is 90% harmless. Japanfreak is right, it will munch on your nutrients a bit (which is the reason it is there in the first place) but there are ways to minimize it. The best pointer I ever received for hempy watering was when you water, pour 20% more than your res will hold in ONE SPOT, as fast as you can.
This will cause the "water table" to rise quicker than your bucket can drain it. The benefit to this is that as your bucket drains, it pulls air through the perlite aerating the roots. If you water fast and the runoff comes out with more force, it will pull more air. The other benifit to this is that it does not keep the surface completely moist. I used to water my hempies like soil, soak the entire surface and let it all drain down, and I noticed that since I have been watering in one spot (I usually water about 1/4" in from the edge) that the top stays drier and the algae is in a smaller spot and dies off before the next watering most times.
Also, once you get a nice canopy going, this will shade the surface of the perlite and not let enough light through for the algae to survive. Of course, growing in small bottles like that you may never get a canopy dense enough to shade, and in that case you could cut round pieces of white paper just big enough to cover your bottle. Poke a hole in the middle big enough for the stem, then cut a line from the outer edge to the hole and slide it over the top of the bottle. When its time to water slide it off, that will stop the algae for sure. For an extra precaution you could even use white on one side, black on the other and have the black side down.
Best of luck
KB