Following PPMs for under/overfeeding warnings

[JoeCollins]

So I am trying to figure out a threshold for differentiating meter drift vs plant indications when measuring PPMs the following days after refilling my reservoir.

Everything on the subject always says that if your PPMs are rising you're feeding too much or if they're dropping your feeding too little. But nobody tends to say how much lower or higher it's actually going when they say "oh well I need to feed it more/less". They don't say their 500ppm went down to 350 or their 500 went down to 545. I'm trying to find the happy medium between chasing ghosts in sensor drift and waiting for the problem to become big enough to be super obvious.

Like I make the reservoir now, and just throwing numbers at the wall, lets say after equalizing for an hour or two my measure the PPM and it is 400.

Now if I come back in 24hrs and that 400 PPM is now 250 I know very well that I have underfed and they need more nuts. I know what to do then and how to get the nuts back up and all. But say instead I measure it after 24hrs and that 400 is now 390. That is not so clear. I personally would call that sensor drift. But I can't figure out where to draw that line so I know when to react.

 

[Mañ'O'Green]

So I am trying to figure out a threshold for differentiating meter drift vs plant indications when measuring PPMs the following days after refilling my reservoir.

Everything on the subject always says that if your PPMs are rising you're feeding too much or if they're dropping your feeding too little. But nobody tends to say how much lower or higher it's actually going when they say "oh well I need to feed it more/less". They don't say their 500ppm went down to 350 or their 500 went down to 545. I'm trying to find the happy medium between chasing ghosts in sensor drift and waiting for the problem to become big enough to be super obvious.

Like I make the reservoir now, and just throwing numbers at the wall, lets say after equalizing for an hour or two my measure the PPM and it is 400.

Now if I come back in 24hrs and that 400 PPM is now 250 I know very well that I have underfed and they need more nuts. I know what to do then and how to get the nuts back up and all. But say instead I measure it after 24hrs and that 400 is now 390. That is not so clear. I personally would call that sensor drift. But I can't figure out where to draw that line so I know when to react.

@JoeCollins Welcome to AFNI have to start by asking why do you think your sensor is not telling you the truth? If it is of any decent quality then you should believe what it is telling you.

Next I am assuming you are in DWC? There are many factors that can and do effect the rate at which your plants can and will uptake nutrients. Make sure the environment is consistent days 78°F, nights 68°F, RH >40%<60% Reservoir Temperature as close to 68° as you can keep it. PH in the range of 5.7 to 6.2. Your nutrients must be in balance. This is why we change the reservoir every week because we have no idea the individual nutrients the plants have been using. Last but not least is to top your PPM of every day with balanced nutrients that match the mix for that week to the starting PPM for that week.

In the past I ran DWC ~600 PPM (nutrients only - not counting the starting water) when the plants were a couple weeks old to harvest. Most days the PPM drop was 200 PPM and I added back the same blend to bring it back to 600PPM. That got to be a PIA so I added a top off bucket with a float valve in the res and by mixing 5 gallons of 30% strength (of the current blend) nutrients the 5 gallon res stayed about 600 PPM all week.

This is what I mean by balanced nutrients:

Tutorial - A word on Nutrients

The proper use of “salt” based fertilizer to grow Auto Flowering Cannabis. Salts: Natural and man made any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation. Learning how to use salt based...

www.autoflower.org

 

[JoeCollins]

Well no sensor gives a single rock solid number, there's always a bit of variance up or down

 

[JoeCollins]

Some lovely help y'all, much useful input. So glad I reached out for help. 0/10 would not recommend.

 

[St. Tom]

Some lovely help y'all, much useful input. So glad I reached out for help. 0/10 would not recommend.

I couldn't help you with this bro sorry but are you on top of things now as mog is are nutes guy and has your drifting stopped I run autopots and my ec never changes with that but I do get odd ph spikes always up never down

 

[Death The Cultivator]

Some lovely help y'all, much useful input. So glad I reached out for help. 0/10 would not recommend.

You need to provide more information. Are you in a recirculating system? Which nutrients are you using? Autos or photos? Reservoir temperature on average? Brand of EC meter? What is your pH doing in relation to your EC, rising or dropping?

I usually let my reservoirs mix, 2 30g/1 55g, for several hours to stabilize the pH and get everything mixed well before I take measurements. Commercially, we let the reservoirs on our 300 gallon tanks mix for two hours before connecting them to the dosing system. In either situation I also keep my reservoir temps below 70f and I also have two HM Digital EC meters that are only off by .1 from each other.

I typically run by the feed chart whether I do flood and drain or drain to waste adjusting the reservoir with recirculating every so often using fresh solution at 50% strength. Have you observed any precipitation? Would need to know your nutrients to be more helpful though

 

[JoeCollins]

You need to provide more information. Are you in a recirculating system? Which nutrients are you using? Autos or photos? Reservoir temperature on average? Brand of EC meter? What is your pH doing in relation to your EC, rising or dropping?

I usually let my reservoirs mix, 2 30g/1 55g, for several hours to stabilize the pH and get everything mixed well before I take measurements. Commercially, we let the reservoirs on our 300 gallon tanks mix for two hours before connecting them to the dosing system. In either situation I also keep my reservoir temps below 70f and I also have two HM Digital EC meters that are only off by .1 from each other.

I typically run by the feed chart whether I do flood and drain or drain to waste adjusting the reservoir with recirculating every so often using fresh solution at 50% strength. Have you observed any precipitation? Would need to know your nutrients to be more helpful though

I don't necessarily have an issue answering additional questions but all your questions are geared towards solving an issue that I have not presented. I'm not asking for diagnosis of a problem and that's all the answers that I'm getting are, attempts to diagnose a problem I have not put on the table. I'm simply asking a logistical "how you manage your measurements" question.

If you measure your PPMs at 400 and you come back whenever you come back and it's 399 I'm sure you don't start adding more nutrients. At 395 I doubt you do either. Probably not 390 either. Same for the other direction. Where is that threshold though. Everybody talks about a PPM rise or PPM drop but at what level of rise or drop do people tend to feel they need to take action.

No PPM either or pH meter is 100% concrete in their number, measure in a different spot in the tank, measure close to the bottom, measure close to the side, wait 10 minutes measure again you're going to have slightly different numbers. So obviously tiny number changes are not reactive to but nobody talks about where the threshold for meter dressed or solution drift is versus a number being something they need to take action on.

I couldn't help you with this bro sorry but are you on top of things now as mog is are nutes guy and has your drifting stopped I run autopots and my ec never changes with that but I do get odd ph spikes always up never down

That's great and all, and I am genuinely not trying to be a butt, but he didn't say a single word to answer my question. I have tried asking this question on like 5 diff forums and every time it's a head bashing experience as everyone "teaches" me everything I could ever want to know about the plants while delicately and complexly avoiding what I was actually asking.

 

[Silver]

I personally never rely on numbers alone Joecollins, I check the colour of the plant AND the numbers combined..

However to answer your question directly..

Generally.. say my target is 500ppms, if they are showing 400-350ppms (or lower) then I will increase the feed, if I start seeing 550PPM+ then I will lower. Hope that helps.

 

[Death The Cultivator]

I don't necessarily have an issue answering additional questions but all your questions are geared towards solving an issue that I have not presented. I'm not asking for diagnosis of a problem and that's all the answers that I'm getting are, attempts to diagnose a problem I have not put on the table. I'm simply asking a logistical "how you manage your measurements" question.

If you measure your PPMs at 400 and you come back whenever you come back and it's 399 I'm sure you don't start adding more nutrients. At 395 I doubt you do either. Probably not 390 either. Same for the other direction. Where is that threshold though. Everybody talks about a PPM rise or PPM drop but at what level of rise or drop do people tend to feel they need to take action.

No PPM either or pH meter is 100% concrete in their number, measure in a different spot in the tank, measure close to the bottom, measure close to the side, wait 10 minutes measure again you're going to have slightly different numbers. So obviously tiny number changes are not reactive to but nobody talks about where the threshold for meter dressed or solution drift is versus a number being something they need to take action on.



That's great and all, and I am genuinely not trying to be a butt, but he didn't say a single word to answer my question. I have tried asking this question on like 5 diff forums and every time it's a head bashing experience as everyone "teaches" me everything I could ever want to know about the plants while delicately and complexly avoiding what I was actually asking.

It was my assumption that by you posing this hypothetical situation you would be able to answer those questions for that hypothetical. I technically answered your question because the EC shouldn't be drifting - hence if it is then those other questions I asked you become relevant. Your EC should not drift, so I provided those example because they are parameters for maintaining a nutrient solution.

Now if I come back in 24hrs and that 400 PPM is now 250 I know very well that I have underfed and they need more nuts. I know what to do then and how to get the nuts back up and all. But say instead I measure it after 24hrs and that 400 is now 390. That is not so clear. I personally would call that sensor drift. But I can't figure out where to draw that line so I know when to react.

My reservoirs are consistent regardless of where I measure because I keep pumps circulating in them, it takes around 30 mins IME for the solution to stabilize but I wait several hours. Once I know the recipe for each reservoir I don't really worry because it should be consistent, so that is also why I asked what equipment you were using to measure.

Your asking a broad question that I'm trying to get context for to discuss with you. All those questions make the final answer that much easier.

 

[JoeCollins]

I personally never rely on numbers alone Joecollins, I check the colour of the plant AND the numbers combined..

However to answer your question directly..

Generally.. say my target is 500ppms, if they are showing 400-350ppms (or lower) then I will increase the feed, if I start seeing 550PPM+ then I will lower. Hope that helps.

Thank you! And yes, looking at the ppm is just one part of the larger equation, I have read tons of literature on the subject and probs watched hundreds of hours of videos at this point but some things like ppms ppl never seem to get into the nitty-gritty numbers with and only give a sky level overview so it had been maddening trying to dial this specific metric in.

It was my assumption that by you posing this hypothetical situation you would be able to answer those questions for that hypothetical. I technically answered your question because the EC shouldn't be drifting - hence if it is then those other questions I asked you become relevant. Your EC should not drift, so I provided those example because they are parameters for maintaining a nutrient solution.

My reservoirs are consistent regardless of where I measure because I keep pumps circulating in them, it takes around 30 mins IME for the solution to stabilize but I wait several hours. Once I know the recipe for each reservoir I don't really worry because it should be consistent, so that is also why I asked what equipment you were using to measure.

Your asking a broad question that I'm trying to get context for to discuss with you. All those questions make the final answer that much easier.

I am sorry but this is just flat wrong. Professionally I have worked with million dollar lab equipment doing QA tests for my job and even those testers have a small percent plus or minus variance for any measurements. The stuff we would use for gardening certainly is not more accurate than that type of equipment. Even beyond the accuracy threshold of the meter, ANY non-static solution is going to have small pockets of higher or slower salinity/ph/temp/literally anything else. There is no such thing as a "perfect mixture" - the variances may be small but they are there.

At the top of this post you can see how to answer the question, it is a very simple question to answer when you don't try to turn the question into more than is being asked. If you are unwilling to give a straightforward answer then NOT ANSWERING AT ALL is a valid option that I encourage you to take.