I'd like to make a small point, i.e. EC is what PPM and TDS are based on, and not every meter brand arrives at PPM or TDS in the same way.
In the Aqua Flakes feeding chart, for the first week of growth, they specify a nutrient strength of 1.2EC and a PPM of 840. They arrive at the PPM, by multiplying the EC *700. Not all PPM meters use 700 as their multiplier.
... I'm using "Aqua Flakes" brand nutes...
When I mixed my 1st batch of Aqua Flakes...
When I measured the EC/PPM in the nutes, it was only 160 or so, and I was told on this forum to keep adding nutes until the EC/PPM was up to about 250-300PPM, which I did...
I changed it today, and mixed up new nutes, and followed the mixing chart exactly for veg growth at 2 weeks as per Aqua Flakes instructions.
...I need a better pH monitor, just using a test kit right now, not a meter...
I then took a PPM reading with my TDS meter, and was shocked to see it is 760!
The water straight out of the RO filter is only around 26PPM before I add any nutes to it.
Why is the PPM SO high, and are my plants gonna keel over now from an over dose of nutes, or should I trust the mixing instructions from Aqua Flakes?
How much should I be concerned about the PPM reading??
What brand PPM meter do you use? What brand TDS meter do you use? (There can be a few extra multipliers for TDS measurements, 640, 650, and 680 are three that I've read about).
What brand do those on this forum, that told you to keep adding nutes until the EC/PPM was up to about 250-300PPM, use?
Most meter manufacturers in the hydroponics industry use one of two conversions, but there are others.
There is the 40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride, conversion which is approximately 700 x EC in millisiemens (mS).
Then there is the NaCl, sodium chloride, conversion which is approximately 500 x EC in millisiemens (mS)."
For instance, the Hanna EC/PPM meters use a multiplier of 500 while the Eutech meters use 640 as the multiplier. My Bluelab Truncheon uses both the 500 and 700 multipliers, with two different values in two separate columns, both read as PPM.
In the Aqua Flakes feeding chart, for the sixth week they specify a nutrient strength of 2.0EC and a PPM of 1400. A Hanna meter would indicate 1,000 PPM for an EC of 2.0. If you raise the Hanna measured mix to 1400 PPM, you've actually raised your EC to 2.8, way too high.
Do you see how the numbers that you are trying to compare via posts, may differ on PPM but actually be the same EC?
The point is to make sure you're comparing apples to apples in order to answer your questions via these forums.
"How much should I be concerned about the PPM reading??
" If you wish to stick to PPM, and as you are using the Aqua Flakes feeding chart, and they use 700 as their multiplier, you'd first want to make sure your meter is using 700 also.
PPM is a valuable tool but when comparing numbers between meter brands, it can be complicated. If you can give and receive your information in EC, you do away with the differences in brands and multipliers.
I hope this helps, just something to keep in mind when comparing posted PPM values to what you read on your meter... 52.
PS, Get a better pH meter.