Adjusting PPM and mixing nutes

First grow is about to go in, everything is finished.

600w HID to veg and 600W HPS to flower, 50L res with 1 plant DWC, cannot wait to see the root ball!

But my questions relate to test equiptment and the such.

I was reading on RIU (cant find it but will) that when you use a digtial PPM metre you need to take into account the scale it reads in as this adjusts your final read out and i should buy an EC metre.
I thought PPM was EC? The thread was talking about hard water and using tap[ water.

Also, if my tap water is 100ppm, do i need to take that into account when mixing nutes, if so, how.

Ive spent 10,000 hours researching everything... Canna nutes, cannazym and carbon dioxide, But im just looking for a discussion on this one as there seems to be no hard and fast rule.

It was something about, when your topping up your res, careful what scale your pen reads in because it will adjust your final ppm reading... im so blazed and cant get my head around it.

I hope ive dribbled enough info for an asnwer.

Ok let's say your goal is 800 ppm and your water source is 200ppm so now u need to add 600ppm of fertilizer to be at your 800 ppm goal. I use a .5 conversion and keep it between 400- 1200 for most strains in veg. Then use ph either up or down

The scale issue for digital ppm readers is that there are two EC conversions -- 0.5 and 0.7. One is more popular in Europe and the other in the US. When asking about ppms, I always state that I use a .5 conversion, and if I'm not sure about the other grower I ask straight out. More often then not, they're using .5, too.

Just like FreeRangeZombie said, if you're looking for an 800ppm max (which is right), and your water is 200ppm, then you're adding enough nutes to your reservoir to take the level to 800ppm, which means you're adding 600. My tap water ppm is 130. So I would add 670ppm to that to get 800. What this meant in reality is that I would mix the nutes per liter as per instructed, and then add some of that to my reservoir until I hit 800. In general, if I mixed nutes at 1/3 strength, that would give me the 670. Try it -- mix a liter of nutes at 1/4 or 1/3 the strength recommended on the bottle and stick your ppm meter in. It should be around that 800 mark.

i would not go over 300 ppm for two weeks then add a 100or so a week you can always add more but if you put to much in you will kill them be over feeding over night be careful the other are correct about haveng to count the ppm of the tap water in the tatol thats why most people start out with 0 ppm in there water so they can get all the nutes in to get to there ppm number