First of all I do not expect people to do anything, I only recommend to either keep (and leave) it simple and pragmatical, or really get to the bottom of the matter which will lead to a second level of understanding. Right I remember now that these tables are also included in the book you mentioning. Wait a sec. and let me check: yes, a bunch of them is provided in version 4.1 I've got here. In the introductions Keith also mentions that one should follow the manufacturers instructions. But what if they do not correspond at all? He also mentions the fact that the composition alters the conductivity of different formulas. He doesn't mention any source for the chart though, so the "credit" goes to him I guess... At page 35 he gives the optimal PH range for most plants with 6-7 but he shows the wrong graphics. Now, that is funny - because what is shown in the book is ideal PH in MINERAL SOILS, not in hydroponics. That was my suspicion anyways: this PH chart and data are probably gathered from various sources and actually those supposed to be optimal in soil culture! There's no way I accept this. This is clearly misinformation, no matter who says or writes it. After that, I don't even want to know who actually came up with the numerous PPM suggestions for these various plants! Here just a few examples how the composition of a formula may indeed influence the EC reading, depending on different ingredients and components and their proportion: 1 gram Potassium Nitrate (very common ingredient) dissolved in 1 liter of distilled water will read 1.25 mS/cm (EC) while the same amount of Magnesium Sulfate will only read 0.6 mS/cm. Thats more than the double/less than half as much. One more major component, Calcium Nitrate will end up in a reading of 1.0 mS/cm. A less frequently and in smaller amounts used but necessary with high Potassium content, 1 gram Potassium Sulphate dissolved in 1 Liter will even be as high as 1,55 mS/cm! (all readings are of specific grades I've tested - results will vary with others and also depend on purity and grade) I am a sceptic for a good reason and I only believe and recommend what I have cross checked myself or what comes from a reliable scientific source I can trust. ;-)

Hi James, I often go for simplicity. Hence, do you actually need to add either ammonium sulphate or calcium chloride, to achieve your wanted- respectively a balanced and adequate formula for your purpose? The amount of ammoniacal nitrate should anyway not be that high and is in most cases covered by the little percentage contained in calcium nitrate (or is supplemented with ammonium nitrate). Hence increasing (or only supplying both forms of) N with calcium nitrate should provide enough N and Ca in most cases. The amount of Sulphur can also be increased with Magnesium Sulphate. A few ppm more Mg in a formula as theoretically wanted, up to 50 ppm is no problem and should make no difference. On top of that, please note that for many crops, calcium needs (actual uptake from a nutrient solution) is often lower than expected or recommended. You could even say that relatively high amounts of calcium in some formulas are simply due to the relatively high content of Ca in calcium nitrate. When looking at your target formula, without even calculating - I can almost tell that you are able to achieve it (or get close enough) without the use of your "additives". And here you should know that a difference of 5-10 ppm in major elements (except P) do not change much (if anything at all) with the effectiveness, grow rate or whatever. Have a look at some scientific research with parts of macro elements in a nutrient compositions. The variables in elemental composition are much rougher (sometimes steps of 50 ppm or more) to get any notable differences. In fact, best accuracy in composing and making formulas is a good thing, because eventually you want to reproduce exactly what you had or modify it accurately. But also keep in mind, that plants do not really require such "human or scientific" accuracy and certainly do not react with some minor differences of a few ppm with macro elements in any final concentration of a formula. They can't even tell the difference ;-)

You can submit your samples of your spent fertilizer solution to a lab if you want to after you get into a routine, and tweak the formula with individual additions, but that is almost definitely not worth the effort with the formula you are currently using because it is specifically designed for lettuce use already and what you just need to do is make sure your water is good and fix the way you mix up the solution. Each week per 160 plants you need to run through like less than a lb. of powder for the three components. Multiply that by 5 weeks, just call it well under 5 bucks a week, that's $25 ,max in nutes per 160 plants, or 16 cents a plant plus the pH down. Check your own numbers more exactly but you might find it even less. If there is a solution problem out of whack it is usually preferible to just change the whole thing and reset everything back to normal in a situation like yours where the non-nutrients in the source water keep accumulating and the plants will appreciate a change as well. But to save some good cash consider a nursery and mature separate section when you outgrow the current pump capacity. Then in the nursery (after transplant from seedlings if you are doing it like that), the first like 10-12 days at 2/3 strength ought to be overall better for the plants and your wallet, and if you could cycle, and in the mature section maybe weekly, keeping in mind that a lettuce bulks up about half of its final weight in the last week or so. You're already making some nutrient additions sometimes when you top off which is an efficient use of the blend the general idea o get everything out of the nutes you can before tossing them. Just guide yourself by the idea that each lettuce sucks up around 5 grams of fertilizer to maturity and if you do it right you will toss out in changes less than another 5 g on all the solution that got spent in its life per head. BTW, I thought I never would grow lettuce and you just got me hooked ;). But fisrt to finish the strawberry NFT, my plugs arrive in 5 days oh crap, see y'all in a week unless I have a problem and then please help (shameless plea now that the pressure is on) This post was edited by PupillaCharites on Sat, Sep 14, 13 at 3:25

Hi Srikanth, Let me try to explain you how a tomato formula is composed in the first place and how the actual concentration needed can be understood in respect of it. There are a few contradictory charts that give ranges of concentrations for various vegetables. But they actually don't tell how these charts were done or on what they were based in the first place. For my understanding, a recommended concentration without a formula is in fact useless. Why? Because it's the other way round, the total concentration is actually the result and total of each element needed and present in a specific nutrient. Have a look at the elemental ppm content of a classical formula for tomatoes, and you'll understand what I am talking about: N: 140 ppm P: 50 ppm K: 350 ppm Mg: 50 ppm Ca: 150 ppm S: 150 ppm You could also use 150 ppm of N and less K (some 280-320 would be sufficient) But let's stick with this formula which is quite generous in K. Anyway this formula has EVERYTHING you need to grow tomatoes and it equals a total of 890 (894 if we include some 4 ppm of trace elements). So the actual recommended ELEMENTAL concentration for tomatoes (not seedlings but maturing plants) is roughly between 900 and 1000 ppm with this formula. Much less of any element would probably not be sufficient and anything more would actually be a waste of resources and money. Why? Because if you do raise the concentration of the solution, you'll raise the content of every macro nutrient (and T.E. as well) gradually. More than 150 ppm in N would most probably induce too vegetative growth, over 50 ppm of Phosphorus wouldn't be of any use or good, as it's sufficient anyways. Same for Mg an Sulfur. More than 350 ppm of potassium (K) would just be a waste as well! I could give you an alternative formula, just for fun (and for those who might think that 140 ppm of N isn't sufficient): N: 150 ppm P: 55 ppm K: 320 ppm Mg: 48 ppm Ca: 142 ppm S: 99 ppm For my understanding of things, in both formulas there is EVERYTHING a tomato plant needs. This-one has slightly more N, a bit more P, less K, less Ca, just enough Mg and obviously less (but enough S). The total is only 814 ppm and there isn't much change anyway (except notably lower K). As for the Orchid formula of a total of 360 ppm: I truly don't know how to deliver sufficient NPK (+Ca,Mg,S, etc) with 360 ppm for a tomato formula. No way... But In case you blow it up to some 800+ ppm (instead of the recommended 360) you'll end up with some random- but most probably unbalanced (disproportional) -formula anyway! Most probably to high in N, "overdosed" in P, lack of calcium and Mg and S, and no idea how much P. I wouldn't do that it any case ... As for other recommendations: I wonder what could possibly be added to the formulas I've listed, to reach 1400 or even those 3500 pm!? ___________________________________________________________________________ PS: For those who have followed recent threads about the difference between elemental ppm content of a formula and ACTUAL total EC/TDS reading when measured with an instrument-> The actual TDS/EC reading of both formulas shown here would be around 975 and 1090 ppm, respectively EC 1.9 and 2.2. Not based on LEC calculations but simple empirical tests I did perform to get the difference between elemental content of a formula in use and actual reading of my instrument. In simple words, when dissolved in water, in an actual nutrient solution they would actually give a reading of EC 1.95 and 2.18 - or the equivalent in ppm when converted 500/1.