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[TUTORIAL] Kill Hydro Slime w/ Compost Tea


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Deep Water Culture or DWC for short is one of easiest, highest yielding methods in hydroponics. It is also unique in that roots are suspended in water for their entire lives. That is why the plants grow so large so fast, but it is also a weakness.

Among those weaknesses are:
- It uses a large volume of water and because of that, it also uses a large amount of nutrients.
- Plant sites are heavy, usually too heavy to move when full.
- Water must constantly be aerated, requiring powerful air pumps to be run 24/7.
- If using a RDWC (Recirculating Deep Water Culture) then a water pump must also run constantly to keep nutrient levels the same in all plant sites. All of these pumps can raise your electric bill.
- And last but not least, all of that standing water creates a perfect environment for brown slime algae (aka cyanobacteria) to thrive.

The slime starts out as a clear snotty film on roots, airstones, pumps, or anything else in the system that is underwater. It quickly turns into a white thick snot that will latch on to your plants roots and from there, suffocate them. In as short a time as one week, roots can go from healthy to a brown rotting mess. Needless to say, this is death to the plants above.

I have had the slime appear in bubble cloners as well as my 40 gallon RDWC. In a RDWC, this bacteria (that lives without light) can destroy an entire crop. But fear not, there is a way to kill it and as a bonus, you plants will grow even faster than before.

This is how the slime first makes itself known in a nutrient reservoir. The pump was thick with slime, clogging the flow of water.

Here is a picture of more an advanced cyanobacteria infestation. This was at the end of a grow and as you can see the slime has turned into a thick brown ooze. The only thing that prevented the pump from clogging was a filter bag.


Firstly, I take no credit for this discovery. I found the recipe while researching this problem. I give credit to a grower named Heisenberg at RIU. If anyone wants the link to a 100 page thread about the tea just message me.

Step One is to clean all of the slime out your system. Empty the reservoir. Take out your plants with slime on their roots and put them in a clean bucket. Scrape all slime out of the plant site bucket. Hold up your roots and spray them down with either some diluted H202 or I also like Physan 20 (a fungicide). You can also let your roots soak in a diluted solution of Physan 20 and water for 24 hours if you really want to kill those nasty bacteria.

Step Two is to make the compost tea. This tea will be different from the kind you can buy at the hydro store. It will be organic in that it will contain microbial life and fungi but will not contain any plant food. So do not add any kelp or any organic nutes. Also never ever add organic nutes in DWC. If you want to go organic hydro then you should switch to ebb and flow or another method that doesn't involve complete root saturation. Additionally, no matter what the salesperson at the hydro store tells you, never add enzyme products like Hygrozyme to a DWC system. It will make the cyanobacteria reproduce like they're on fertility drugs. Do not add bloom boosters either or the same thing will happen.

Get a bucket (could be five gallons, could be fifty, it's up to you), fill it with water, add an airstone, and get some bubbles going. RO water is best, but not necessary. Also don't think that RO water will prevent slime from growing, it won't.

Use one handful (per gallon) of General Organics Ancient Forest. This stuff has 30,000+ strains of beneficial bacteria. Put this in a tea bag of some kind. I use paper towel tied up into a teabag. You can also just dump it in a bucket and strain it later. You could also combine some stuff from a local garden store: earthworm castings or peat humus. If you only have earthworm castings, those will do in place of Ancient Forest.

Put in some Great White or other product that contains mycorrhizae, beneficial bacteria, and trichoderma. Mycorrhizae is a symbiotic fungi and that keeps crud off your roots. You could certainly just use this alone and see improvement. I use about a half scoop for five gallons of water.

Add about one capful of Aquashield (liquid compost). There are other brands of liquid compost available as well. This is the starting point for the microbe reproduction process.

Add a few drops of Molasses so the microbes have some food. For five gallons, I add about a teaspoon.

The ingredients.

Let this brew for 48 hours then add it to your res and plant sites. You can give about one cupful per gallon. Keep it in the fridge (it lasts 10 days) and keep adding a cup a day until it's gone.

There are other products you can use such as GH's Subculture B and M, but I don't have experience with them. The recipe above is fairly cheap considering what you get out of it. The microbes brewed in tea will be more numerous than if you just add the ingredients to your res. Do not add Ancient Forest to your DWC, that part you have to brew as a tea. Even if you are lucky enough to not have the slime you will get improved yields by adding compost tea as the beneficial bacteria and fungi help the roots take in food.

Tea brewing. Sometimes a froth appears, sometimes not. It doesn't matter either way.

I make a new batch of tea every two to three weeks. When I begin a new grow or change a res I always add the tea. When starting a new grow, add nutrients and pH down first and then add the compost tea. The reason is the acid in pH down can kill those microbes you just spent two days producing.

If you toss in a sponge or porous rock in the plant site or res, it will give the microbes a place a hang out.

Before long you will have beautiful healthy roots like this!
Edited by Nix
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Interesting read . My water requires in one small set up for 3 to 4 plants I use nothing but PH down everytime I feed and add water for evaporation . I have almost 3 gallons a week of it in one ebb and grow tray set up . I never figured out where that water evaporates too I have no problem with humitidy on that floor . I hate the slime . I keep it in control no problem in winter using a little bleach that a co op in California taught me to use with Jacks Classic ( micro amount clear flush before harvest ) but when summer comes and water temps increase it can be a bear . I may have to pay someone to help vent my room this year . I have been using Fox Farms Peace of Mind with my dirt plants and Sunshine # 4 mix so I understand now how much the microbes can help and you just have to get down a repeatable routine . Thank you .

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I haven't experienced bad tasting meds from using peroxide. I haven't heard anyone speak of it before either. Hydrogen Peroxide degrades to become water and releases the extra oxygen molecule in the process. It doesn't seem like peroxide would make meds taste bad.

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I have just experienced brown slime algae. I lost almost my entire crop before I discovered the tea brew. 6 weeks after trying what seemed like everything to stop this ferocious

killer, I read on some forum about this tea you speak of. Wow I finally see white roots again and the plants are growing again. I was just about to post a thread like this. Thank you Nix for your post and I hope anyone who may have this problem will try this tea. It was a great eye opener for me.



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Anyone know if this be brewed on a sort of perpetual basis?


I just brewed up a 5 gallon batch and used about 4 gallons. It occurred to me that perhaps I could add more water to the remaining gallon and some more molasses and just start the process over with the 1 gallon being a starter.

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  • 1 year later...

Doing this saved my garden folks.


h202, SM 90 , physan 20...all will not work well.


After months of fighting...this is the only thing that has worked for more than 5 days. Though I am using a different recipe that produces the same thing.


If you are like me and thought that this might be a pain in the arse, or that it would not work, I am here to tell you that it is simpile, cheap, and I suspect it will increase my yields.


If you have root rot in hydro do yourself a favor and try this.

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While you are fighting the infection add back 1 cup of tea f per day. I am adding 1 cup per day in each site, and the rez.

From Heisenburg on RIU

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 also okay to give the dying roots a slight tug to see if they come off. Now let the roots soak in 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.

*** The smaller your roots, the less likely the are to survive a strong h202 treatment. In my experience using h202 will increase your recovery time.

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 water is often a losing battle. In fact, since most hydro sterilizers fail to kill this stuff, when you sterilize the water you are removing competing microbes and opening the field to slime. 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 microbe tea with a diverse selection of organisms 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. (Aquashield can be replaced by any inoculation that contains bacillus 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. (ZHO can be replaced by any inoculation that contains myco fungi)

Ancient Forest ($14) - Soil amendment provides a high diversity of microorganisms, including more than 35,000 species of bacteria and over 5,000 species of fungi. (AF can be replaced by any earth worm casting)

EDIT* Mycogrow soluble is the cheapest and most diverse inoculant we have found. It can replace everything here except the ancient forest.

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, just don't overdo it. Now take an old sock or pantyhose and fill it with about 2 handfuls of EWC or Ancient Forest. 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 or even an aquarium net. Next, add about a tablespoon of molasses to wake up the microbes and give them something to eat. 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. If you use EWC you will probably notice a foam eventually, this is normal. After 48 hours you can 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. Fresh tea can have a range of smells from earthy to mossy to shroomy. Bad tea smells like gym socks, fecal matter, or decay.

Initially, add about 1 cup to your res for every gallon of water, and then add 1 cup total every 3 days after. If you can, pour a little over the base of the stalk to inoculate the root crown. 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 multiplying the microbes this way your products should last a great deal longer. Once you have eradicated slime and simply want protection from future outbreaks, adjust the tea dosage to 1 cup per 10 gallons about once per week.

If you are interested in why the tea works, or what products you may use for substitution, continue reading the rest of the thread. It is a journey I took with others to learn a great more about the tea. If you want to see how I use this tea in a cloner, jump to here.

***In an attempt to address frequent issues which bloat the thread

You can substitute just about any product you want. Any EWC will give you a good base of microbes. Any product or combo of products which contain mycos, bacillus, and trichoderma will do the trick. Don't worry about matching my exact ingredients. The exception is AN microbe products. Stay away from AN microbe products!

If you notice a dark sort of slime form after you treat with tea, stay the course. As long as you see new shoots growing you are on your way to recovery. The after-slime is harmless and will not expand or stall roots. New root tips are what you want to see.

Do not use tea with h202, sm-90, Zone or any type of sterilizing product. Do not filter tea beyond 400 microns.

If you have slime attacking plants with very small roots, adding housing to your res like a lava rock or koi pond mat will make a big difference. Place the housing in your tea brew for the duration and then move it to your res.

No one has reported sprayers clogging from using regular tea. But, if you are concerned you can also try aquashield by itself without brewing. High pressure nozzles will kill most microbes, medium pressure and simple sprayers are fine.

Take care of impropoer res conditions FIRST. Even the tea will not save you from disease if you do not have enough oxygen or proper temperatures. Res water should be around 75f with bennies. Air pump should be at least 1wt per gallon. Light proof your buckets!

If this solution works for you please post in the thread and tell us your story.

I'm happy to answer questions in the thread. You will get a faster reply here than messaging me. Remember, all advice I give is intended for a synthetic DWC grow.

Some FAQ's

Can I run a perpetual batch of tea?

No. The key to fighting slime is a diverse microbe population. No matter what you do to your brew, diversity will peak and begin to decline around the 48 hour mark.

Can I feed the bennies in my res instead of letting them die and replacing them?

No, you would be feeding the slime as well. Some bennies will live on in your roots, most will die. It is simple to replace them which we do every three days while fighting slime, and about once a week after the slime is gone.

Will the chlorine/chloramine in my tap water kill off my bennies?

It is best to use pure water to brew the tea, however adding tap water directly to your buckets in small amounts to top off will not kill enough bennies to matter. I add as much as a gallon of un-aged tap water to my 5 gallon res with no ill effects. If you are worried, simply add a little tea a few hours after watering.

Can I add too much tea?

As long as your tea is brewed properly it is really hard to add too much.

I added tea, maintain proper res conditions, and still have slime!

First be sure you are not simply seeing after-slime. (see above) If it is aggressive slime, then you are probably adding something organic directly to the res. Check each and every thing you put in your mix, and be sure foliar sprays do not drip into the res. Incorporate some type of housing into your res, such as lava rocks.

You are not teaching us how to breed microbes, only multiply them.


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