Is 650 ppms out of the tap ok for tomatoes in recirculating DWC

happyhydroApril 26, 2010

This is my first post. I have set up a recirculating deep water system outside in five gallon buckets to grow tomatoes for the first time. I put 12 plants in 2 weeks ago and they look very happy so far.Have been mixing well water @650 ppm with RO water @ 100ppm to about 350ppm.Is this necessary or can I grow in straight well water @650 ppm.I am scared of getting nute lockout because of too much calcium. Thanks alot.

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grizzman

could you get by with a nutrient formula that contains no calcium and let your water take care of it?
you say your well water is 650 ppm. do you know what compounds are producing that concentration?
you could try mixing a test batch of straight well water and nutrient concentration then let it sit a few days and see if you have anything precipitate out of it.

    Bookmark   April 26, 2010 at 2:54PM
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lucas_formulas

May I respectfully ask "what ppm"?
As there is quite a difference between ppm measured with a 500 or a 700 conversion rate instrument and it would again be different with analytical data provided by an official analyses. Well yes, 650 ppm measured with a Hanna/500 instrument would equal 1.3 mS/cm and if measured with a Truncheon/700 instrument it would equal a actual reading of 0.92 mS/cm.

In fact both are high, but while 0.92 is upper borderline, 1.3 is what I'd call inacceptable for base water of an appropriate nutrient solution.

If well water has that high reading (either figures), it's generally (if not mainly) caused through high amounts of calcium among others like Mg, Iron, Boron, and quite a multitude of other often usable elements etc.

High calcium in well water may indeed interfere with any acidic components that come with nutrients, but the high PH-buffering capacity of high calcium content in water is in fact the actual downside. Many people experience problems with the later, as the calcium prevents acids from getting the PH down to ideal but bouncing back until it is dissolved with several acid applications.

Best is anyway to have rather pure base water with poor mineral content and use nutrients that provide 90 % of the ions and not like in some extreme cases 50% or less combined with a unknown (very mineral rich water). Some of the calcium in your well water is usable by plants and some isn't. Be sure that the part that precipitates after a day or two, or the one that would be competing with some PH-down will not be available.

How comes that the RO water varies between 100ppm to about 350ppm? Is that your average measurement or is this a factory specification which would depend on kind of mineral content. I believe this isn't standard data for RO. Most clean RO water should be much less loaded , more around 50 ppm or so.

Anyway, I'd absolutely stay with the RO water and well water mix, perhaps use even a higher quantity of RO water if your nutrient provides enough readily available Ca .

    Bookmark   April 26, 2010 at 10:14PM
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happyhydro

Thanks for the comebacks, grizzman, I am trying your experiment,Mixed well @540 with grow nutes to 1140ppm.After 24 hours it was down to 1040ppm and now after 30 hours it is back up to 1100! Whats up with that? Lucas, The gauge is a Hanna Primo cheapo.It calibrates to 1382 and can measure up to 1999ppm. Sorry to be unclear. the RO is consistent at around 100ppm and I have been mixing with well to 350ppm for a starting point before adding nutes. If, as you suggested,I go with more RO and less well, what would you suggest as a good starting point andwhat would the numbers be for a nutrientprofileusing a calmag supplement andnutrients.For the record I set the ph of this system 3 weeks ago to 6.0 and it it still 6.0. Much obliged!

    Bookmark   April 27, 2010 at 5:13PM
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lucas_formulas

Putting all facts together, you have happy looking plants a stable pH, which means that the calcium part is fine with your own mix of waters (which is indeed something I would always recommend). Hence I wouldn't change a thing, not even adding CalMag or anything else. Don't change a winning team, as they say.

As for the conversion rate of your instrument, it's for your own good to know it and to always tell it in the same time you exchange "ppm data", or ask for second opinions. As far as it concerns your daily measuring it doesn't matter as it is your working unit ;-)

As for the drop and climb of EC, ppm with your test, it's probably due to evaporation (precipitations should be visible) and some delayed PH-change that follows evaporation. PPM/EC reading varies not only with temperatures, but also with pH.

    Bookmark   April 27, 2010 at 9:22PM
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