So I’ve got questions on ppms. As far as I understand it ppms is a representation of the amount of dissolved solids (mainly cal and mag) in the water. I read feeding cannabis with hard water is bad for it and can easily cause nutrient lock, for instance my water from my hose and my sink are both above 500 ppms which is considered extremely hard, so soft water is prefered. But then I read that ppm’s should be at ranges of 200 during seed, 800-1000 during veg, and 1200-1500 during flower. What should my ppms be going in during these phases and what should I do about my hard water situation?
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PPM stands for Part Per Million, in this context is the total amount of dissolved salts including Macro (NPK) and Micro (Cal, Mag, Zn, S, etc.). Hard water is a problem since it contains a huge amount of Non-Dosed salts. Which is undesired since we want to give the plant the right amount of nuts of each Micro and Macro elements.
To avoid this, growers use RO (Reverse Osmosis) water, basically filtered tap water having a little amount of elements. Then they add the desired dose of bottled nuts. Or you can buy some decent water.
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Since RO is basically void of all nutrients how do I go about amending that for watering. Should I just do straight RO one watering, test that run off’s ppm’s and feed next time if necessary. Or could I do like a 1:4 mix of tap to RO water. Also what should I shoot for my ppms to be when going in during the different phases. I’ve read ppms should be higher going in than coming out but that doesn’t really make sense to me
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You should choose a nutrient line such as FF trio or Jacks321 and follow their feeding schedule. Once you have RO water, you use only that one. You mix the nutrients doses in the RO water.
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You couldn’t truly test a waters ppm for r/o or distilled you’ll come out with inaccurate readings since there’s nothing to little to read.
Always add cal/mag first then your remaining amendments
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Okay so cal-mag every water in, and nutes as needed shown by ppm level of the runoff?
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When you pour in your feed the plants roots and media capture some of that nutrition as it passes through. These plants are very aggressive growers and take a bit of feeding. Some of that feed will sit in the soil/coco and get used later which is why we feed, water, measure ec/tds then feed again if needed. If it’s higher coming out than going in then you have an issue as your soil is rich and could lead to over feeding and possible toxicity
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One big question is…what soil are you using ? Some soils like FF ocean forest. You won’t need to feed till approximately week 6. Any soil that is “hot” (a lot of nutrients), doesn’t require feeding while they are young. Check runoff ppms around week 6 to see what’s left in the soil and then Start feeding as needed
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One thing when taking measurements is to remember what scale you’re using.
For example, when using fox farms trio you want to measure in the 700 scale. From what I understand most of the other nutrient brands use the 500 scale. Each scale is checking for different salts, that being said, a ppm meter is truly measuring the EC of the water and multiplying that by 500 or 700 depending on what scale you’re using.
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Good point…that’s absolute correct. I use ff dirty dozen pack. Their feed chart list in 700 scale, I have a 500 scale meter. I can’t remeber who it was…but a nice gentleman found me a 500 scale for fox farm.
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Nice to see this still circulating. I made that in microsoft paint, lol
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So you’re the nice gentleman? Lol.
Sorry I forgot who gave it to me and I couldn’t give you the recognition for giving it to me. But there been all the of bowls since then lol. I got it printed out and hanging over my mixing station. 
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It’s no longer mine. It’s the community’s. I was hoping it would make the rounds because it was becoming a chore to explain the 700/500 scale for fox farms without a visual representation, lol.
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Well the community appreciates it… I know I did
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Oh okay, what do you mean by scale? Is it like you have to adjust the amount of added nutrients because of the amount of ppms your water. So since my water is around 500-550 ppms I would be running nutes for a 500 scale?
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@Gooseman1324
Each nutrient line uses a different ppm scale for reference. I use fox farms trio which they want you to use the 700 scale when testing ppm.
So on your EC/ppm meter, make sure you’re in whichever scale your nutrient line suggests.
From what I have heard and have seen on here, most use the 500 scale. That being said, somewhere on your nutrient schedule it should tell you which to use.
Hope this helps.
If your water is near 500ppm, stick your meter in and switch to EC. If your EC is close to 1 then your meter is a 500 scale meter. If the EC is close to 0.7 then your meter is on the 700 scale.
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It just depends on how your meter was calibrated/designed from the manufacture. When we measure salts in the soil, we are measuring EC ( electrical conductivity). The meter will automatically take the EC number and turn it into a PPM reading. The problem is, some meters take the EC and times by .7(700 scale) and others by .5 (500 scale). So if your meter is 500 scale and you are following a feed chart that is in 700 scale, then you nutrients will not be at the correct ratio. So if I have 500 meter and you have 700 meter, our readings won’t be the same while testing the same solution. Most feed charts I have seen have been in 700 scale, like the fox farm that I use. @BobbyDigital explained this exact scenario to me in the past, and he graciously gave me a fox farm feeding chart that was for 500 meters. I have posted it earlier in this thread. Hope this helps.
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Okay so when the ppm’s are higher coming out than going in then my soil is full of the nutrients it needs, roger. So does this rule of having it be higher going in then coming out only apply to when you’re feeding it nutes? I use Fox Farm Ocean floor which runs pretty hot from what I’ve been learning. I just started a new plant on Sunday and tested the runoff ppm’s right away before adding the seed. PPM’s in were around 520 and coming out they were around 1361 so obviously I’m not about to give my little baby seed 1360 ppms worth of nutes, right?
So the point I guess I’m trying to make is that ppm’s going in should be higher than coming out only after the soil has been depleted and needs added nutes? but not for just a regular watering?
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