Salts Build Up and PPM

Are “salts build up” just excess nutrients or are the nutrients some how altered and unavailable to the plant? Could I just lower my incoming PPM and utilize the lower number to hit my target ppm and the “salt build up” is also used?

Example: I want 1000ppm in the roots. My runoff is 1200ppm. If I watered with 700ppm, that mixes with the 1200ppm, my new concentration is some number lower than 1200? Or must I flush the 1200ppm out and start anew?

I understand pH lockout, I’m not confused there.

Thank you for any insight!

It’s not that precise. You’ll get a feel for maintaining proper PPM within experience. Sorry that isn’t so helpful.

Yes, the fertilizer salts build up over time. A salt buildup will drive pH down and make pH hard to manage. Some nute brands are worse than others about salt build up. Fox Farm nutes are probably the worst for salt buildup.

I flush when I am unable to manage pH.


Okay, thank you!

So the term “salts build up” really means unused nutrients? They still can be taken up by the plant but they just haven’t yet? And unused nutrients can alter pH as they sit unused? Sound correct?

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Yes, unused. Plants use nutrients in the form of dissolved solids. What happens with a salt buildup is that those nutrients solidify and bond to the soil. They are no longer “dissolved solids” and are thus unavailable for the plant to use. The salts are liquefied by watering, but it isn’t an efficient way for plants to get nutes. Once there is a salt buildup that makes pH hard to manage, it is best to flush the salts out using a wetting agent such as Sledgehammer or Florakleen and a lot of water. Soils that are buffered for cannabis will return to a pH of ~6.5 with a good flush. Flushing also washes out all of the nutes, and you are typically left with a runoff PPM of 300 to 400 after a good flush. It’s important to feed again after a flush, but keep in mind that wet soil won’t absorb nutes very well. Give a full feeding again after the soil has dried.


Thank you.

I’m trying to figure out the best way to flush out Hempy Pots. This will be challenging as I added a bit of worms castings and I don’t want any water, mixed with the castings, reaching the wicking chamber.

Can’t help there. I’m not familiar with Hempy Pots. The information I provided is for a soil grow. Hempy Pots seem to be a form of hydro, which has different requirements for pH and so on.

You might find a search of the site to be helpful.

Soil Grower FFOS and blends.
I have avoided “flushing” or wetting until 20% RO (as I am a chronic over-waterer, trying to reform).
Saturday, I watered until 20% RO was perceived. The PH measured on more than one plant RO was 8.5.WTF? Panic for sure, and 2 gallons of 5.5/1000 BLOOM and we are done for the day. Nobody appears to have been drowned with 2 gallons used for flushing EACH plant. Previous feeding method was top dressing FFOS and blends, just prior to flip. Good buds being developed 3-weeks now, so feeding was in order. Tent temp usually 80-degrees for lights on (off 65-degrees). LED lighting totals about 1-Kwatt. RH average 50% lights on (off 70%). Buds starting to get slightly-sticky.
I welcome helpful suggestion for Wednesday watering/feeding. Fan leaves and some bud removal to favor or remove competition. OUT of space in tent.

I have never had a issue with salt build up and I have been using only use Fox Farms products. I have only flushed one plant in 4 years with Sledgehammer and it took 5 days to dry out.

Now I have see others have issues with this. But not me.

I had to flush at least twice per grow when I was using the Trio. pH would get out of control.


Why 1000? You have added worm castings to the coco so it will naturally be higher than the input ppm. Is the plant exhibiting problems? What is pH of the runoff? And what is feed pH? How do you get runoff from a Hempy Bucket?
About root zone buildup and bottom watering systems, autopot directs its users to not top feed after bottom feeding starts. I believe the reason is to prevent pushing salts that are carried to the top by the wicking action back into the root zone.

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No problems at all. I’m just trying to understand a solution should this problem arise. 1000ppm was just a simple number to use if my question didn’t make sense or wasn’t clear.

I just collected water from the drain hole when I was filling the pipe.

I didn’t check the runoff pH, but pH going in is 5.8. TDS going in is anywhere from 950 to 1100ppm. The TDS out was 1235ppm.

I’m running 1 Hempy Pot as a test to see if I want to move to this method. Here’s how it looks so far. I’m 21 days into flower and I was thinking I might try a flush before going the rest of the way. Maybe I’m over complicating it!


Not me and you have seen my handy work with the entire FF nutrients to not using any at all.

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I wouldn’t flush, she looks good!!


Yeah, I’ve used FF nutrients and burnt the crap out of 2 plants. It was my own fault. Got cocky and didn’t fully read the instructions. Took some serious flushing. Saved 1 but the other just seemed to freeze in time…then died. Live and learn.


@Autofreak I had to also learn trial and error using FF products. But after using them for 4 years, its no long trial and error.

I am debating on if I want to use nutrients on this grow cycle. The last two with nutrients used only one time for the entire grow is some pretty frosty and tasty smoke. :+1:

I’m trying a do over with the 2 strains I fried. This time I’m only using molasses water and cal mag if needed. Just to see if it was the strain. Plus, I shall not be defeated. :rofl:


I’m about to flush for the first time because of salt build up in week 8, how much should I feed her after flushing?

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Your a helpful guy . … you have Lor of good information.