Help, slime is killing my seedlings!



Grow start date: 1/9/2017 - planted Ice in 1" RW
1/12/17 - Ice seed sprouted
1/14/17 - placed Ice in DWC; planted WWxBB in 1" RW cube
1/19/17 - WWxBB seed sprouted
1/20/17 - WWxBB placed in dwc
Strains: Nirvana Ice; White Widow x Big Bud hybrid (can’t remember the seed bank at the moment)
Space: 4x2x7 tent inside indoor closet
**Method:**DWC/ scrog- top feeding by hand w/ H2O from res until roots emerge from net pot
Light cycle: 18/6
Lighting: 600W Viparspectra LED, 19" away from seedlings
Reservoir: two 5-gallon buckets w/ 6" net pot lids (Lowe’s blue buckets)
H2O Aeration: 1- 9" RedFrog aerator + 1-2" air stone per bucket
Fans: Exhaust - Apollo 6" 440 CFM Inline Fan w/ 6" Carbon Filter (placed outside of tent for more space); Intake - passive vent at bottom of tent
**Air Circulation:**1- 6" clip fan (non-oscillating) & 1 - Honeywell Turbo Force Air circulator Fan
Nutrients: GH Flora Trio, RAW solubles OminA, Ful Up and Sea Kelp; and HydroGuard
Reservoir PH: 5.5-6.5 (struggling to keep within 5.5-6.5 range)
Tent Temp & Humidity: 71-82F / 52-69%
Reservoir Temp: 73-75F w/o frozen bottles and 61-69F w/frozen bottles
Reservoir H2O change: every 7-10 days
Water: pH adjusted DI and sometimes tap

What’s up guys! This is my first post here after many months of silent browsing on the forum. I must say I have found lots of helpful and insightful information here. I can’t wait to get more experience under my belt like many of you. Im posting because I am having an issue with a recurring slime contamination in my dwc reservoir that i can’t seem to get a handle on. Like i said it is my first grow so I am learning while doing most of the time. However I have read multiple posts online on how to deal with this in setups like mine and cannot seem to solve my issue. I have tried reducing reservoir temperature, adding preventive i.e hydroguard, using quality water, add more aeration but NOTHING seems to help. I thoroughly disinfected my setup for the second time this past weekend to no avail. I used bleached but made sure to rinse it completely out of both buckets and all my other equipment.

I’ve been careful to keep net pot lids on buckets when adjusting pH etc. but today I notice the gunky slime in the bottom of my net pot. My seedlings are just babies they are going on 2 and 3 weeks from seed. Because of all of the issues Ive had with pH and temp fluctuations from day 1, their root systems are weak and underdeveloped. They still have yet to grow out of the net pots into the nutrient water!!

Tonight I am going to wrap my blue Lowe’s 5-gal buckets with Reflectix insulation and do another reservoir water change. Hopefully this will fix it once and for all. After cleaning everything, I will wrap buckets, adjust water to 5.5pH, and add 30mL of 3% H2O2. Will run for about a day and if things look ok will add nutrients back. I may not add any nutrients at all, at least until i see more root formation. So far plants have only received 1/8th of recommended nute dosage. Does my current plan of action make sense? Is there something better that I should do to fix this? I have been using frozen plastic 1 liter juice bottles to help with res temperatures. I wish I had a better way to do but this is what I have for now. I know I could buy a chiller but don’t have the space for that, not too mention its expensive for a small grow like mine. Any helpful suggestions or comments are appreciated, please do share your thoughts.


This slime is algae get hydrogaurd that should fix your problem


I have it already and use it at every res change. Algae keeps coming back.


19" sounds close for seedlings. Just something to maybe keep an eye on.


Ok, have you tried a splash of hydrogen peroxide (3%)


Yes, I have tried h2o2 also. I have added 30 mL to the res (3.5 gal of water) and ran it for a day or so before adding low nutrient dose but the algae has shown up again.


Thank you I will do that.


What distance would you recommend?


Ok hang on ill take some one that will be of better help meanwhile waiting on @Hammer to show up ill do some digging on this @bluefly28


Thanks so much!


Thought about it, likely this is your cause res temps should be 66-69 degrees, if any thing try to keep it around there without fluctuations, meanwhile ill continue to dig on this and my pleasure


The problem that you will run into is the fact that algae and marijuana prefer the same environmental conditions – where your marijuana plants will thrive, so will algae. They like water that is rich in nutrients and has light permeating through it.

For that reason, you should make sure your hydroponic equipment, including tubing, buckets, and reservoirs, is not completely clear but instead is made of an opaque material. Rock wool, a substrate used in hydroponic setups to support marijuana roots, is also a popular gathering place for algae.

Since algae need light to grow, you can take care of it through the control of the lights. This is not to say you should dim or turn off the lights – this would also have a negative effect on your light-loving plants!

Instead, make sure your equipment is dark opaque in color, and try covering your rock wool with a landscape fabric. This will give the rockwool some space without allowing light to permeate through.

Once you see algae growing in your hydroponic or aeroponic system, you should clean your entire system and remove anything that is made of a clear material – replace them with an opaque version of the same thing. If you don’t have the money or time to replace them, you can also just try simply covering the clear equipment with some sort of dark material. If the algae are in the water itself, you can try a few other methods for clearing things up.

First, simply rinse out and clean the reservoir. Mix hydrogen peroxide (H2O2) with water at a 1:10 ratio. If you add this to the reservoir in minimal amounts but fairly often, you will give the roots of your marijuana plants an oxygen burst, giving them the ability to fight off algae growth. Because hydrogen peroxide can harm the roots of your plants, you should only do this for plants that are older and more developed since they can better withstand some harm.

If you use UVC lights in your system of filtration, micro organisms will be caught before they even make it to the grow room. These are the same types of lights that are often utilized with hot tubs, aquariums, etc. It won’t harm your marijuana plants, just like it won’t harm humans or many aquatic creatures. It will, however, take care of any potential algae problems.

Another method you can try using is grapefruit seed extract, which is actually used by many cities when treating their drinking water, as well as a natural way of handling the algae problems in fish ponds and lakes.

A final method that might work for your hydroponic reservoir is a barley straw mat. It’s an organic way of controlling algae in places like lakes, ponds, and other bodies of water that have the potential of algae. It is not an exterminant, so it won’t kill the algae that are already there. Rather, it slows down algae growth while not having any negative effects on any of the “good” organisms living there (including your marijuana plants).


Whatever your manual says. I have 900’s that say 30"-36" above. But, the ILGM guys have you covered. They’ll be sure to mention if you should move the lights or not.


If they are 19" id move them to 24", if its a cob led you can get away with it being 18" above


@bluefly28 3 thing’s id recommend do not use the peroxide and hydrogaurd at the same time . alternate them . next i’d use black buckets not the blue the blue will allow light in to a small amount . and last ( just my thoughts ) no more sea kelp in hydro .



I would have to say that the buckets aren’t the problem… I have ran full Cycles in white buckets and had no problems as far as algae… in my temperatures are in between 75 and 80 degrees with no problems … im running Hydroguard and orca and my nutrients are GH nutrients … I would think if he’s having problems he’s using organic nutrients which don’t really go well with Hydro… from what I’ve been able to tell… just my 2 cents…



I used the Lowe’s blue bucket and they are thin walled allowing light through.
Wrapping the bucket or replacing is a good start.


How often is it 73-75 compared to 61-69? …that could be issue ?


You could probably use a better (higher output) air pump for more aeration in the reservoir. I’ve run hydro for a while now and never ran into algae. Keep up with consistent reservoir changes and always use HydroGuard (unless also using peroxide). The blue buckets may be letting light through also, so you might want to wrap that just as an added precaution. Are you physically cleaning the buckets in between the water changes? I personally do every time I do a water change, another preventative measure I take. I hope this can help you out dude, I hate hearing about algae problems!



Hello guys, I apologize for the delayed response. I have come down with a terrible cold and was in bed a good bit of the day yesterday. Thank you all for your insightful responses. I have managed to make a couple adjustments in my setup based on what you’ve suggested and other things I’ve read. I plan to get rid of the algae in a two part solution. I think I may have lost one of my babies to the overall issue. The Ice seedling’s first leaves have turned yellow and dried up but its 2nd set is still green with only a slight yellow ting on the tips. I don’t know if it will bounce back so Ive kept it going but something tells me its a goner! But anyways here’s what Ive done so far…

Part I:

  1. Washed buckets and aerators with bleach. thoroughly rinsed everything before reassembling
  2. Cleansed all the visible slime from net pots by spraying with a high pressure shower head. I know there may still be some inside but hoping to take care of that with Part II
  3. Wrapped buckets with Reflectix. Put reflective tape on one bucket to see if it would make difference in maintaining lower temperatures. I usually find that the temp has increased to 73-75F when I check res in the morning due to bottles melting o/n. I know I could solve this by using bigger bottles or changing them again during the night. Well the latter solution is a no go because I am a heavy sleeper and getting up in the middle of the night isn’t practical for me. The larger bottles will take up too much space in the res and will block my circular Redfrog aerators (I’m contemplating to discontinue using these, they don’t seem as strong as I’d like).
  4. Placed buckets back in tent on top of concrete paver’s stone. I’m hoping the concrete serves as a heat sink for each reservoir.
  5. Added fresh DI h2o pH 5.5, cal-mag (wasn’t too sure if i should’ve waited for this but went ahead), and hydroguard. I did not use H2O2 this time at all! No nutrients were added only running H2O.
  6. Added newly frozen H2O bottles to each bucket
  7. Raised LED to 24"

Part II: had to order a few items for this so will pick up with this once everything arrives in the mail.

  1. Make a microbial tea consisting of Hydroguard, Extreme Gardening Mykos, and EWC
  2. Add 3 cups to reservoir on Day 1 and afterwards 1 cup every 3 days
  3. Add more tubing between pump and reservoir. Hoping this will allow time for air to cool down some before reaching reservoir water. I believe this is also a heat source. Currently using an Ecoplus 18W industrial pump. It puts out a lot of air but it’s very loud and I hate that about it. Will later try to figure out a way to quiet it, right now its suspended from a shelf outside of grow tent. I noticed placing the buckets on the concrete has seemed to help with the noise level some.