DWC PPM Question...

420n00b said:

So I'm growing with a 5 gal. bubble bucket. Not experiencing any problems with my plant but I'm not sure about the ppms in my nutrient solution.

I monitor PPM and PH with a Hanna tester. I've calibrated it according to the instructions that it came with and I honestly don't think thats the issue.

My tap water measures around 130-140 ppm out of the tap. I'm using the fox farms nutrients and following their schedule. Currently on week 2 of full strength nutes and my ppm measures between 750-800. Fox Farm feeding schedule says it should be around 1120-1260. Yes, I am adding the correct amount of nutes based on the amount of water in the bucket.

Am I doing something wrong? Will the low ppm slow/stunt the growth of my plant?

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• If water levels drop from day to day and PPM's stay the same you should be stoked because they are eating and drinking at the same rate. Add back full strength nute solution when you top off and keep PPM's the same.
• If water levels stay the same and PPM's drop then the plants aren't so thirsty (high humidity/low temps?) but they are still eating the nutes and life is good except your water is weak!!! Calculate how much nutes you would have to add back to get the PPM's back up to normal, pull out one gallon of water from the tank into a bucket, add your nutes, stir and take a PPM reading. If your PPM's are high that's a good thing. Pour back 1/4 into the water tank, mix, take a reading and it should have climbed 1/4 of the way up to where you want it. Repeat until your PPMs are perfect (if you calculated right you should have added everything back).
• If water levels drop and PPM's climb, your plants aren't eating and something is wrong. Most likely a pH imbalance (assuming your daily visual inspection of your grow does not show other problems such as slime, temps, etc.). Find out what the issue is, correct it, then readjust your pH back to 5.8.

jsgamber said:

Realize that the 1120-1260 assumes nothing else but the recipe in the water less your starting PPMs. If you are adding supplements such as Cal/Mag, ...zymes, SM-90, sugars, etc. those will bump your PPM up as well as affect pH, and you need to know those numbers!

So Dude if your environment is perfect and you have no observable issues it means your girls are eating and LOTS by the sound of it. That's the reason you have a PPM meter is to determine what the changes are day to day, so you can monitor trends in your plants, blah, blah, blah. What was the PPM reading two weeks ago when you originally mixed everything up? Time to open up Excel and create a daily log.

Realize roots CAN and are selective of what nutrients they take up vs. when they take up water and they don't always happen simultaneously. Here's the rule of thumb:

• If water levels drop from day to day and PPM's stay the same you should be stoked because they are eating and drinking at the same rate. Add back full strength nute solution when you top off and keep PPM's the same.
• If water levels stay the same and PPM's drop then the plants aren't so thirsty (high humidity/low temps?) but they are still eating the nutes and life is good except your water is weak!!! Calculate how much nutes you would have to add back to get the PPM's back up to normal, pull out one gallon of water from the tank into a bucket, add your nutes, stir and take a PPM reading. If your PPM's are high that's a good thing. Pour back 1/4 into the water tank, mix, take a reading and it should have climbed 1/4 of the way up to where you want it. Repeat until your PPMs are perfect (if you calculated right you should have added everything back).
• If water levels drop and PPM's climb, your plants aren't eating and something is wrong. Most likely a pH imbalance (assuming your daily visual inspection of your grow does not show other problems such as slime, temps, etc.). Find out what the issue is, correct it, then readjust your pH back to 5.8.

So which of those items sound like you?

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420n00b said:

All good info so +rep for that. I should have said earlier that when I change the rez I use a freshly washed bucket that is clean and dry. I am using a six inch net pot that hangs about 4 inches into the bucket. Since the plant is only about 2 weeks old and the root system still small I have to add almost 4 gallons of water to get the level up to my roots.

With that in mind...when I add fresh nutes to the new water and take my ppm measurements it's only 750-800. I do realize that they should drop as the week goes on and the advice about keeping the log is good and I'm going to start doing it.

Why is the starting ppm so low?

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jsgamber said:

More than likely due to differences in your meter and the manufacturer's. Who know's maybe they use 400 PPM tap water and forgot to account for it? If your plants have adequate daily growth with healthy green leaves, no cupping or yellow/burnt tips, then why break what's already fixed? I found my adjusted PPM's are 150 higher than the label and at full strength my growth is lush. I even experimented and tried to push up 150 more beyond that and it's when the tips started to burn. So even though I mix up a batch of 1200PPM nutes according to recipe, it still ends up at 1350 and I happily live with it because my notes tell me so!!

So as a controlled experiment, see if you can "push" the nutes up by 1/4 more and observe your new growth over the next few days. If they burn, then you know you are at the limit. If they don't burn, then I'll leave it to you if you want to push them more.

Only you know what works best in your environment.

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