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Help with DWC nutrients and EC/TDS, brown sludge


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I recently started monitoring the EC/TDS levels in my DWCs after I realized the GH nutrient chart I had been using (for some time) was for a “drain to waste” setup. After finding the “recirculating” setup chart, I was surprised to see that the nutrient amounts were significantly different. For example, the recirculating chart shows a nutrient ratio of 10, 10, 5, whereas the drain to waste chart shows a ratio of 4, 5, 1. 

On top of using the wrong chart, I only use half the strength recommended throughout. Despite all this, over several grows, some have been amazing and trouble free and some have been much more torturous. Obviously, there were many other factors involved throughout these other grows, as they were not all identical strains, grown in identical conditions, etc - they were just all grown with the same setup. So the nutrient question remains.

The setup:

Basic DWC setup, 6” baskets with hydroton
Air temp is around 75
Water temp is around 70
Humidity is about 50%
Using 600w MHs on 24 hours a day
Water is from the tap (always has been) - runs about 350ppm
Nutrients are GH trio
Also add Hydrogaurd at about 1ml/gal
pH is kept around 6
Water is changed every week

Current plants are 12-15” tall and look very healthy for the most part. Some are growing much better than others (there are a few different strains). There has been some slight yellowing of a few leaves and brownish sludge continues to appear on some of the roots - another reason why I started looking into EC/TDS levels.

I changed the water a few days ago with this new found nutrient info. These plants are in mid/late veg. Instead of adding 2, 2.5, and 0.5ml/gal of GH micro, grow and flower like I normally would - I added 5, 6 and 2ml/gal (half the GH recirculating chart values). Hydrogaurd still added at about 1ml/gal. That said, the TDS reading after adding these nutrients was about 1100ppm. The water alone has a ppm of about 350. From what I’ve read a good rule of thumb is to have ppm values of 600, 900, 1200, 1500, etc for vegging week 1, 2, 3, etc. I assume this is starting with a pure water value of zero. So at this point, I would be looking for a ppm around 1200. However, with my water having a ppm of 350, a reading of 1100ppm would really mean only 750ppm are nutrients - which is still significantly less than recommended. Right?

Am I looking at all this correctly??

Should I be adding even more nutrients? With everything in seemingly optimal range and I keep my buckets clean, why am I still getting brown sludge on some roots? When I lift up the baskets and the roots are moved around a bit in the water, some of the brownish stuff falls off the roots and has a powder consistency in the water. Some new roots are growing through the brownish stuff. It just doesn’t look healthy. 

Thanks for the help guys!!! (Sorry this got a bit long).

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Take the fertilizer manufacturers directions with a grain of salt. Less is usually better than more.

It sounds like the beginning of root rot. Rinse the roots off in running water.Change the water and don't put any nutes in right away. Add some 35% hydrogen peroxide to the water and that should help. Start gradually adding nutrients again when the plants show signs of improvement. Cooler temps help out too. Root rot likes it hot.

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I would also back off on the lighting.  Most studies indicate that s plants in veg can not benefit from more than 18 hrs of light.  Ditto on the peroxide Bill mentioned above.  If you are not familiar with it, peroxide it comes in a 3% level from the drug store, but you need the 35% from the hydro store.   Put it in at about 2ml/gallon.   

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I will cut back the lighting. I have read about using h2o2 to battle root rot. However - since I am already using Hydrogaurd, adding h2o2 as well could destroy everything. I’ve also read that h2o2 should only be used very short term on its own, cuz it kills the good bacteria as well as the bad. I am hesitant to use it in conjunction with the Hydrogaurd.  If this is total hogwash, I’m all ears. 

Thanks guys!

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