When a clear snot forms on roots in a DWC, and the normal course of treatment for root disease doesn't work, you probably have something called brown slime algae, which actually isn't algae at all, but a cyanobacteria. It loves oxygen and doesn't need light to grow. It doesn't care if your res is chilled or not. Safe levels of H202 slows it a bit but doesn't cure it. It can show up for DWC growers for no apparent reason even after years of successful grows. Once it shows up it's often a nightmare to get rid of. It WILL eventually spread to other DWC tubs, although it almost never gains a foothold on older well developed healthy plants/roots.
Several root conditions will cause a slimy build up; doesn't mean you have the brown slime. Common root disease is almost always caused by improper res conditions, and they improve greatly when those conditions are corrected. This isn't true of the slime. When to suspect brown slime algae is when you are doing everything right and still can't get rid of it. People who get this try the normal stuff... More bubbles in the water, cool res temps, and h202 treatments. The slime may appear to be gone at first, but comes back strong in as little as 12-36 hours. It starts out subtle like a clear coating of mucus on the roots with no odor. Plants often still appear healthy for a while, but all root production stops. In a very short time it will cover the entire root base and become thicker and sometimes turns yellow. Eventually it strangles the roots which causes pythium to set in, and at that point turns brown and finally has an odor.
The treatment is to clean up and sterilize the root base, and then populate the water with beneficial microbes. Simply running a continuous sterilizing agent such as SM-90, Zone, ect will almost certainly end with the slime as the winner. Some people have had luck running bleach or physan 20 continuously in the water, but most do not want there plants soaking in these particular chemicals. Making a microbe tea is cheap and easy, and IMO the proper way to fight this slime in a perpetual DWC garden.
Clean up the root base as well as possible. Best thing to do, if you can, is hold the plant over the sink and use the sprayer to vigorously rinse the roots, trying to get all the dead roots and gunk to slough off. It's OK to spray 3% h2o2 solution directly onto the roots at this point. It's also okay to give the dying roots a slight tug to see if they come off. Now let the roots soak in a strong h202 solution, or a mixture of whatever sterilizing agent you have. Physan 20 works great. This is a good time to sterilize any equipment and give the res a good scrub. After a few hours, no more than 12, of soaking in the solution rinse the roots really really well again, prepare a fresh res, and inoculate the res with beneficial microbes. Wait another 12 hours before adding nutes.
Once the slime is gone be sure to practice proper res maintenance, which includes keeping any type of organic material out of the res. Trying to sterilize the res is often a losing battle. In fact, since most hydro products fail to kill this stuff, when you sterilize the water you are removing all competing microbes except this one. There are people who use RO filters and then run their water through a UV sterilizer and still end up with the slime. The answer always seems to be beneficial microbes.
Below is my previous introduction to preparing and applying a microbe tea.
In DWC the roots sit in water constantly putting them at huge risk for disease. Some people have great luck using nothing at all. Others find sterilizing products keep their roots white, but a few of us have found that even with proper res maintenance and doing everything right, we still get a slimy build up on the roots. This is when a microbe tea can really make a difference by robbing the slime of housing, food, and actually attacking it.
By making a compost tea with a diverse selection of microbes you will have a super tonic for you res that will ward off nasty gunk and build up while at the same time keeping your roots stimulated and growing. Best of all it can be made for just pennies per batch.
Ok so we wont be starting from scratch. You have to buy a few products. But instead of using the products directly in the res, you will be breeding them in a tea. This way, you can use a fraction of the regular dose and make your products last much longer. Plus, you will end up with a freshly active tea that is more diverse than anything you can buy on the market.
Aquashield ($12) The product composition consists of: Bacillus subtilis, Paenibacillus polymxa, Bacillus circulans, and Bacillus amyloliquefaciens. This gives you a base population of beneficial bacteria.
ZHO Powder ($10) The product composition consists of: Glomus intradices, Glomus aggregatum, Glomus etunicatum, Glomus mosseae, Trichoderma harzianum, and Trichoderma koningii. This gives you a base populartion of beneficial fungi.
Ancient Forest EWC ($14) - Soil amendment provides a high diversity of microorganisms, including more than 35,000 species of bacteria and over 5,000 species of fungi.
The recipe is really simple. Start with non-chlorinated water. I make 2 gallons at a time, but you can easily adjust the additives for whatever amount you wish to make. Now put the water into a bucket and throw in a couple air stones. The more air the better. You want the water to be almost turbulent from the bubbles. Now add 15-30ml of aquashield and about 1/4-1/2 scoop of the ZHO powder. You will be breeding these into the billions so it doesn't really matter how much you start with. Now take an old sock or pantyhose and fill it with about 2 handfuls of EWC. Tie off the sock and place it in the water above an air stone, or better yet, feed an air stone down into the sock itself. If you want, you can just throw the EWC directly into the water and strain it out later with cheesecloth. Next add about a tablespoon of molasses to wake up the microbes and give them something to eat. You could also use any sort of bud sweetener. We will only be feeding the microbes in this tea; never add food for the microbes to the res itself. It's okay if the bennies in the res starve. You will be replacing them every few days. Now let the tea bubble at room tempeture for 48 hours. It can be used after 24, but will be more active and diverse at 48. You can now store the tea in the fridge where it will stay fresh for about 10 days. Once it starts to go bad it will develop an odor. If you ever detect an odor from your tea, throw it out and make a new batch.
Initially, add about 1 cup to your res for every gallon of water, and then add 1 cup total every 3 days after. Your water might get a little cloudy but your roots will stay white and stimulated. When you use tea and practice proper res maintenance you can feel confident your roots will be healthy. By breeding the microbes this way your products should last about 5x longer. Once you have eradicated slime and simply want protection from future outbreaks, adjust the tea dosage to 1 cup per 10 gallons.
If you are interested in why the tea works, or what products you may use for substitution, continue reading the rest of the thread.