New EC / TDS pen Mentoring request

[TommyT]

I just bought a new Vivosun EC / TDS tester.
I tested my water with and without my fertilizer and I am at a loss of what to do next.
They all seem way too high.
Here is what my tap well water tested at:
PPM 468
EC 917

My RO water:
PPM 16
EC 40

I have been using 1/2 well water and 1/2 RO water mixed together to water my plants:
PPM 290
EC 567

Those numbers didn't look too bad but here are the numbers after adding my Dyna-Gro nutes.
I use this chart:


Now here are the numbers after adding the nutes:
6.5 ph
EC 1565
PPM 782

I usually also add 4 teaspoons of Epsom salts per gallon :
6.5 ph
EC 3490
PPM 1750

Can someone with experience please help me with this?

[Sage]

is it possible the calibration is off?

[TommyT]

is it possible the calibration is off?

I suppose that it's possible.
They claim that it comes pre calibrated.
Also I know that my well water is really hard. I had a test done about twenty years ago on my well water.
And the RO measures only 16 PPM. So that seems about right.
I not saying that it's not out. It just seems correct without the nutes.

[TommyT]

BTW, there is also a 500 and 700 scale for ppm, this may be throwing your numbers off as well

A quick read - https://support.bluelab.com/hc/en-us/ar ... they-mean-

You also want to subtract your starting number from the final total. The problem with a ppm so high at the start is that you do not know what makes up those ppm.

This one does both EC and PPM. So it's doing the calculation.

It's this meter:
https://www.amazon.com/VIVOSUN-0-05ph-A ... 7384&psc=1

[TommyT]

When I add a tablespoon (roughly 5 teaspoons) per gallon of epsom salt, it usually gives me a ppm of around 1000. This seems to be around the same difference in your ppm

So...
Now here are the numbers after adding the nutes:
PPM 782
I have been using 1/2 well water and 1/2 RO water mixed together to water my plants:
PPM 290

782 minus 290 would give me 492 which I guess is about right. Maybe even a bit low.

Then after adding the Epsom salts it is 1460 PPM.

[TommyT]

OK
I did the math and my meter seems to be using the 500 scale.
I looked it up and the Dyno-Gro chart uses the 500 scale also.
So at least I'm using the correct scale.

[Treetrunk]

I use a similar meter. Its sometimes called the Hanna scale.
What base reading does the nutrient company recommend?
With my hydro set up my tap water is 130ppm and I add calmag to bring the base reading to 300ppm.
Then add the nutrients after subtracting the base reading.

[Treetrunk]

Just had a look at the Dyna gro website.
They recommend a base ppm of 50.

[TommyT]

@Treetrunk Thank You for the info
I should have mentioned that I'm in soil.
Do you know if those numbers would be the same for soil?

[Treetrunk]

http://www.organicagardensupply.com/dyn ... ule-chart/
Base ppm of 50 according to the chart.
I'd either try the well water with half nutrients or just use the RO water and follow the chart.
With my chart for Canna aqua you can alter the base from soft to hard water.
I add calmag to get the water to hard and then add nutrients.