# Dark Green/Brown growth forming on top of Rockwool



## elgrecko23 (Sep 18, 2009)

Hello all. 

I posted this in the sick plants forum at first, but was sent to this section by a more experienced MP member    Thanks again HIE.

I have a drip hydroponic system right now and am experiencing what I am assuming is algae, but fear may be mold on all four rockwool blocks of my small setup. I also see small white specs. Could this be nutrient/salt build up? I've attached some pictures here for reference of the build up and of the leaves. 

Setup info: it is a drip system with CFL lighting. The drip runs for 15 min three times a day. The blocks stay moist, but don't appear to be too saturated. Right now the plants are about a month and a half old and are between 1 and 2 feet in height. The 4 x 4 rockwool cubes sit in 1.5 gallon pots with hydrotron clay pebbles. I'm using Canna Aqua Vega nutrients. The temp in the room stays between 75 and 90 and the area was thoroughly cleaned before setup. I have an Eva dry dehumidifier, Air purifier and small oscillating fan. The lights are on a 24 hour cycle right now for Veg stage. The leaves are all solid color and appear to be healthy, aside from the growth on the cubes. However I do see small brown spots at the base of the plant stalk. Is this normal? 

I read up and feel that this is probably algae and that covering the blocks from the light should help, but am worried I'm about to start dealing with mold attacking my babies  

I could use some expert advice.  

Thanks in advance for the help.


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## garden_engineer (Sep 21, 2009)

yea.its algai,they sell block covers to avoid this problem.they'll be fine,just get some of the block covers.i think i payed a few dollars for 20 or 30 of em.


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## stonedrone (Sep 21, 2009)

you can just cover up the cubes with more of the clay pellets


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## iceman423 (Oct 1, 2009)

or instead of paying for the covers; use some of the left over mylar or b/w poly (if you have some) and cut out a square with a hole in the middle for the plant.  thats what i did on a constant flow system.


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## Tater (Oct 2, 2009)

Or buy an ozone generator and learn how to safely use it.


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## The Hemp Goddess (Oct 2, 2009)

The tops of the rockwool cubes should always be covered with hydrotron to prevent this.  Put the cubes into the buckets with the bottom of the cube sitting on the bottom of the bucket and then fill with hydrotron.  Rockwool will always grow algae on top if exposed to the light.


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## StoneyBud (Oct 2, 2009)

The Hemp Goddess said:
			
		

> The tops of the rockwool cubes should always be covered with hydroton to prevent this. Put the cubes into the buckets with the bottom of the cube sitting on the bottom of the bucket and then fill with hydroton. Rockwool will always grow algae on top if exposed to the light.


:yeahthat: :yeahthat: :yeahthat:  Listen to the Hemp Goddess! 
In addition to what she has so wisely said, the surface of the hydroton should be about 2 inches above the highest fill level of the nutrient solution. This keeps the hydroton from having the same problem. When using rockwool, just put it at a level where the lower half of the block is in the nutrient solution at it's high level. The block will wick what it needs initially.


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## Tater (Oct 2, 2009)

Lots of good answers there and all of them will work well.  The long and the short of it is you need to create an environment in which algae will not thrive.  This essentially means dark.  Algae will not grow without light, mold however will.  Which is the reason stoney mentioned the wicking.  Do not EVER let rockwool sit in water (well besides when you are prepping it of course) it will lead to plenty of maladies.


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