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#1 FITN

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Posted 17 March 2019 - 12:00 AM

I've been growing in kratky containers for maybe 3 or 4 months now. Up untill a few days ago I've been crossing my fingers when it comes to ph and PPM levels as I had no way to check them. I just purchased a inexpensive ph meter and a TDS meter. From a small amount of research, it looks as though I'm supposed to be around 5.5 for ph. Does that sound about right?

I am coming up short on PPM research though. Does my PPM level after I add the nutriants depend upon what it is coming out of the faucet? An example would be that straight from the faucet, it reads 200 and I need to add a level of 500 so I'm look for the meter to read 700. These numbers are just for an example, I'm just not sure what level I should be shooting for when mixing nutes.

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#2 sinensis

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Posted 17 March 2019 - 02:21 AM

From a small amount of research, it looks as though I'm supposed to be around 5.5 for ph. Does that sound about right?


sounds ok, but maybe research more and wait for others to chime in
 

I am coming up short on PPM research though. Does my PPM level after I add the nutriants depend upon what it is coming out of the faucet? An example would be that straight from the faucet, it reads 200 and I need to add a level of 500 so I'm look for the meter to read 700. These numbers are just for an example, I'm just not sure what level I should be shooting for when mixing nutes.


yes, TDS depends on your starting water. and theoretically, distilled water should have a TDS of 0 ppm.

PS: since you say you are short on research, i say this just as an FYI, not to 'correct' you...
your meter is really measuring EC, not TDS. if it's giving you "TDS" instead, it's really giving you an estimate based on EC using a conversion factor, and you need to know which conversion factor it's using if you want to 100% understand what it's telling you.
 

imo, in gardening applications, people should just speak in terms of EC so everyone's on the same page.

one guy's "TDS" isn't necessarily the same as another's "TDS", and you won't know unless both specify the EC -> TDS conversion factors they're using.

 

this can serve as a decent primer: http://www.scielo.or...502015000400008
 
my research has come up somewhat short as well. here's some of my ramblings when i was playing around with kratky (which i've sort of abandoned):
http://thehotpepper....-noob-concepts/
 
in particular:
 

i don't really understand the implications of EC beyond trying to use it to get some idea of nutrient concentration. i've read some posts with rhetoric about "don't use tap water as it will count towards your EC" as if to say that all contributors to conductance have an equally meaningful impact on plant health. i've probably misunderstood it? i don't get why we're looking at EC all the time instead of just relying on initial gravimetric and volumetric measurements (or better yet, testing for individual nutrients). what can EC tell you if you don't know what's contributing to it? is there some overall upper limit for EC where plants tend to get sick? if anyone can point me in the right direction, i'd appreciate it.  :think:


Edited by sinensis, 17 March 2019 - 02:24 AM.


#3 Masher

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Posted 17 March 2019 - 06:59 AM

Ph 6.0 to 6.8 for established plants.

It's not weed, so 5.5 is below proper level for best uptake of nutes at 5.5 for vegetable/fruiting plants.


Ppm...if water is 200 and you need 500, then yes 700 is correct

#4 FITN

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Posted 17 March 2019 - 09:40 AM

I did come across EC while looking for information of PPM levels for Kratky. I didn't pay it much attention as I thought it was a totally different reading. Am I actually looking at an EC reading if the digital readout on my TDS meter says PPM? I took a reading of my tap water this morning and it came out at 114ppm. Taking that into consideration, what reading should I be looking for when I mix my nutes in, to have it at the proper concentration for a established plant?



#5 sinensis

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Posted 17 March 2019 - 02:43 PM

if you have some time, read the study i linked to in my last post. the one about south african mine water.

 

these "total dissolved solids" ("TDS") meters are really electrical conductivity (EC) meters, not TDS meters because that's what they're really measuring.

i am writing "TDS" in quotes to imply that it is not really TDS.

 

it applies a voltage across two probes with known characteristics separated by a known distance and from that it gets the fluid's conductivity.

 

after that, it multiplies it by some number (conversion factor, f) to give you an estimated "TDS".

 

example: "TDS" = EC * f

 

two problems with this.

 

1) it's a lie. the "TDS" (usually in units of ppm) it's showing you is almost never an accurate representation of the TDS of your sample.

one kind of dissolved solid will have a different impact on conductivity than another dissolved solid. pH can affect the conversion factor also.

those conversion factors are commonly determined only for specific dissolved solids (like NaCl for example). if you're measuring a sample that has only distilled water and table salt in it, then it will probably give you a good idea of TDS. if your sample is something else, then the "TDS" value it displays is nonsensical.

 

so if you know what your conversion factor is, you can just do EC = "TDS" / f

 

2) two "TDS" meters (even if properly calibrated) won't give the same reading unless they use the same conversion factor.

that conversion factor i mentioned? there's no standard value for it used by every meter. when you're talking "TDS" with your buddies online, the figures you're sharing and comparing are meaningless unless you're also specifying the conversion factor used by your meter (or by your manual calculations). many meters say what it is in the user manual, but many don't (especially cheaper ones).

 

for these reasons, it makes more sense to just give EC guidelines and not even talk about "TDS"

 

---

 

and how is true TDS really measured? you take a sample and dry it gently in an oven and then weigh the solids that are left over.

 

--

 

also, sorry for derailing you. i hope your kratky gardening goes well.


Edited by sinensis, 17 March 2019 - 02:51 PM.


#6 FITN

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Posted 18 March 2019 - 12:41 AM

No worries, I don't feel derailed at all. It just seems as though everyone who grows some form of hydroponics recommends checking the nutrients strength when mixing and PPM is number attributed to that strength/concentration. I'm just try to do what I can to get the best results. You haven't derailed me, just a lot of info to soak in.

All that being said, I did find out that my TDS meter converts EC to PPM using the NaIC formula. I found this chart to help with the different formulas. So now I should be able to find the EC based upon my PPM readout but I'm still unsure of what level it is supposed to be to ensure the best growth for peppers.

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