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Old 11-21-2010, 11:04 PM
GpsFrontier GpsFrontier is offline
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Join Date: Mar 2009
Location: Lake Havasu AZ.
Posts: 1,855

I always try to stress observation of the plants as the most important factor in knowing how they are doing. Just like you noticed the leaves starting to become yellow. I used to mark when I changed the nutrients on the calender, and/or added anything to it (and still try to). But after forgetting so many times, I mostly just rely on observation to tell me when to change them. Although knowing when it was changed last is still important, because as you get used to knowing how long the plants can go without problems (including pH swings), signs of early problems can be a singe of other issues.

The roots looked nice to me. Although I did see some slight brownish, but that is not necessarily a sign of any problems. Older roots will tend to become brownish naturally, also the nutrients in the solution tend to stain the roots the older they get. As long as you are continuing to get good new growth, and the new roots are continuing to grow out white, and the older roots are not turning dark brown, as well as the tops of the plants are looking good, then that wouldn't be anything I would worry about.

If they do start to turn dark brown, the two major factors that I know of is "lack of oxygen in the water", and "excessive nutrient temperatures". Of coarse dark brown mushy roots could be caused by pathogens that can cause root diseases also, as well as fungal diseases, but I have not ever come across that specific problem. Like I said, I clean and flush my systems to prevent that sort of thing. But I have dealt with "excessive nutrient temperatures" (I live in the mojave desert). But I would consider the two major factors first.

I always keep an eye on the nutrient temp just in case, it should be be between 68 and 72 degrees Fahrenheit optimally. Above 80 and your likely to see signs of browning as well as dissolved oxygen loss in the water. Below 60 and the plants wont be able to absorb the nutrients as well, and your likely to see signs of stunted growth. Because I grow outside my nutrient temps have ranged from 110 in summer, to about 38 in winter, so I have seen extremes and dealt with both.

I also add H2O2 (hydrogen peroxide), not really for pathogen/fungal control, but for adding extra dissolved oxygen. But it can help reduce the number of pathogens in the solution also if you ever come across it. I use 1 tsp (5mL) per gallon each week (when I remember). Sometimes I forget when I added it because I didn't write it down, so I will wait to add more so I don't add too much in too short of a time.

P.S. Just thought I would mention that when I flush my systems with straight water with each nutrient change, I usually just run it through a couple of cycles (30 min each or so). Then sometimes I empty that out and do it again, before emptying that to add the fresh nutrient solution. But I don't think flushing it for 24 hours will hurt anything.
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