[GpsFrontier]

Hello jhinkle,

Funny you ask question #1 -- about changing out the nutrient solution. I read a paper from cornell univ:
http://www.greenhouse.cornell.edu/cr...ic-recipes.pdf

I spoke at length to Dr. Cari Peters on that subject. Cari stated that changing nutrient solutions was necessary when the fertilizer being used was not properly designed for hydroponics and overtime the nutrient ratios would change as some were consumed faster than others.

I grow lettuce and tomatoes and asked specifically about those two. Cari stated that Jack's 5-12-26 + 15-0-0 calcium nitrate did not require changing except at the end of the growing cycle. Cari stated that the nutrients in the hydroponic mix was all soluble and mixed in the proper ratios to make intermediate changing not required. This is my first try at tomatoes so I will see how well things work out.

I wasn't there for your conversation. but I'm sure there are a lot of miscommunications for one reason or another. Large commercial growing operations can get away without changing the nutrient solution for two reasons. But neither of them are in your favor. Commercial operations can get around this by either running their system as a non-recirculating system, or lab testing the plants and adding back only the specific elements the plants use faster/more of. Your system is recirculating, and you don't have the ability to test and only add back specific mineral salts. Every time you add nutrients your adding ALL of them, not just the ones the plants used most of. It doesn't mater how properly balanced the nutrients are designed, plants don't use the nutrients evenly no mater what. Eventually your nutrient solution will become unbalanced, leading to toxic buildup of nutrients that the plants don't use as much of.

You can reduce the effects of nutrient imbalance for a specific time frame by using nutrients designed for a specific crop like tomato's. But you cant change it without changing the nutrient solution, running it as a non-recirculating system, or lab testing and only adding back the specific mineral salts the plants have used. For the home grower lab testing is to expensive and not cost effective. So that leaves either changing the nutrient solution regularly, or running it as a non recirculating system.

One sure sign you need to change your nutrient solution is the rapid pH swings. That's why I asked how often you change it, because you were experiencing them. But before I gave any advice I wanted to know if this could be related to expended nutrient solution, or something else. That's one of the reasons I asked about this. The other reason is if your nutrient solution is unbalanced, you could be experiencing any number of nutrient deficiencies and/or toxicities as well. How often you should change the nutrient solution depends on a lot of variables, but mostly depending on the size of the plant compared to the water volume. I wrote an article "What size reservoir do I need" to help explain these things.

The Cornell paper -- 360 grams of each are for 100 gallons. Jack's blog states 368 grams.

Just for future reference, I always recommend asking the nutrient manufacture only because I want the information to come from the horses mouth. So I'm not really interested in what Cornell says, but if JRPeters has a blog that gives this information that's fine. I usually e-mail them the question directly to make sure I understand correctly. I'm not really familiar with grams, but if the grams to ounce converter I used is correct, 368 grams is about 13 oz. That seems a little high to me, I know what your using is a different formula than the herb formula. If it were me, I would e-mail them just to be sure.

I'm right on the ocean - 85 to 90% is what weatherbug states.

I asked about this for two reasons. One is the spots could be fungus, one is more common in dry climates, but humid climates are more susceptible to fungal growth. The best defense against fungal growth in humid climates is good air circulation. The other reason I asked about humidity is to find out if spider mites may be likely in your area. While I'm not sure how many species of spider mites there are, I think they all prefer hot dry climates. But I could be wrong.

Questions 5&6 -- I just went out and cut every stem that had white marks on them. I brought one inside and looked at it under a microscope. It looks like patches of small spider webs. You can smear the white spots - as is you are collapsing the web and smearing the strands together.

This leads me to think your experiencing either a fungal growth, or spider mites. Spider mites are very small and hard to see with the naked eye. Usually you don't even notice until there's an infestation. If left long enough, the webs will become very noticeable that they are webs, and usually when you become aware they are there. Under a microscope a fungus can look like tiny hairs/webs, but unlike actual spider webs, a fungus is more localized like growing spots, and not warped around leaves and stems.

The reason I suggested to pluck the leaves and get rid of them by either putting them in an air tight bag (like a Ziploc) or burning them is the only sure way to keep either fungal spores and from spreading, and/or spider mites from migrating. Even if you place them in the trash unless their contained spores can become airborne, and spider mites will crawl out to find somewhere else to go near by.

The best defense ageist insects is a healthy plant. Insects are drawn to plants with their defenses down first. Their looking for an easy target. But if you notice their a problem with insects, first you need to identify what you have, in order to deal with the. Tomato horn worms are hard to spot at first, but will be unmistakable when you notice your leaves being eaten down to the stem. Tomato horn worms don't leave white spots, they eat the whole leaves.


Let me know if you think the spots appear to a a fungus instead of spider mites. I have some articles saved on dealing with fungus that I could post for you.