Using a TDS meter after a month of growth from seed.... WTF?!?!

So I've begun to train my plants with LST after a month from seed. Some plants are more developed than others, one isn't tall enough to begin training compared to the others. Now that I'm getting some smell from the tent and they've been developing in their 5 gallon fabric pots I've decided to try out giving them nutes.

I'm using Growth Technology Grow and on the label it says to add nutes to water of 1.5 mS/cm. I am using this TDS pen after a GC member recommended it to me to use with UK tap water.



I used the following website to convert 1.5 mS/cm to 960 ppm TDS.

Conductivity convertor, Siemens into TDS PPM and MHO

So I stick the reader in and it gets to 621. When I add nutes it jumps up and so I begin to water it down. The reading I get is something like 005 with a x10 underneath. EH?>!?!?!?! So I am guessing it's 1005 ppm TDS so I think that I just need to water it down a little. So I add water in tiny bits at a time and it goes like this

005
004
003
621

Is my TDS meter broken or am I totally missing something? The nutes are obviously very strong but diluting with water has a much more accommodating margin for error.......... however with the way it was watering down you'd think I was adding in tons. The huge jumps are making no sense and are really doing my head in as maths is something I don't find hard...........

I reset the test by adding another 500ml of water to bring the concentration down. My readings were adjusted with a 1/4 teaspoon of nute.

530
550 + 1/4 tsp
577 + 1/4 tsp
609 + 1/2 tsp
003 (x10 underneath reading)

If this is metric it should go up to 999 right? When I search up TDS meters websites say they go up to 999......... someone please help as this is INSANELY frustrating.

 

Hey there GG!

When you say start off at 500ppm do you mean the strength of the water as they've not had nutes before instead of jumping straight to 960? If I need to "train" the plants on the nutes what is the rule of thumb for increasing the concentration over what time period?

I understand that 5x10 is 50 but if you keep adding nutes how does the concentration go from 609 or 621 in other tests to 003 or 004 respectively? It's becoming more concentrated! So how can you be 621, add a tiny more nute and then be 003 (x10)? Surely you've gone up as you've added more despite the reading being lower if it's 30? Plus the manual says if it's got x10 underneath it has to be over 1000.......

I just dipped the pen into the solution again. I took the batteries out to "factory restart it". The reading climbed from 555, 580, 605, 621, 002, 003. Surely this is bonkers? I didn't add anything, just put the pen in.

Lastly the website converter says 1 mS/cm = 640 ppm TDS ..........

1 is 2/3rds of 1.5. So if I want to water down the concentration by a third from 960 that would be 320? Which would then needed to be added onto the water's natural reading which is 328. So I need a reading of 648 to be two thirds of a full reading? Full concentration = 328+960 = 1,288

 

I didn't, but I can run some more water out of the tap to compare. Does the "natural" salts/minerals count towards my total count or do I need to minus it off?

If you are curious the tap water reading is 328

 

x

 

So during veg you just go for the total ppm and don't factor the water ppm in?

Nectar/Mammoth is another brand of nutes I am guessing. What I am googling they seem expensive but aren't as known over here. It's always good to know other brands as I like to read up and compare things.

When you say slurries, do you mean you water your plants enough to make it look like mud?

NFTG is Nectar for the Gods I am guessing? When you say you feed 3 x in a row do you mean 3x per day evenly spread out?

 

I'll try and bullet point my ideas:

- I understand to not jump straight to full strength nute mixtures
- What is the responsible method for increasing nute strength over time?
- If I am only adding nutes to the water, why is the reading increasing to around 600 and then dropping to 30?
- The ppm of the tap water is 328
- Do I need to minus off the ppm of the tap water when calculating my total nute strength with what I am adding to get as a reading?
- The website converter I've used says that 1mS/cm = 640 ppm TDS not 500..... are you rounding down? If so, why?

 

That is a really clever technique for having a true way of measuring if your soil is getting hot! Science for the win!

 

The bottle and a lot of testimonies seem to all have the same idea. Get your plants growing naturally until you are in their final container. I decided to go when I thought that training would be in full flow. So yeah, it would be every feeding but I still can't figure out the odd readings from the ppm meter.