TDS readings off RO water?

Finishing up northern light grown in Foxfarm happy frog Foxfarm dirty dozen nutrients. Stopped feeding three weeks ago trying to get TDS readings as low as possible to harvest.Ph all water going in to about 7.0 to keep outflow at around 6.5.Last feeding TDS was 3000 pH was 6.4 out,Checking outflow every couple of days when I watered TDS went down steadily 2.0 then 1.9 then 1.7 then 1.6 800 then 1.0 1.7 now at 2.0 . I have this on two separate plants just water for two weeks now numbers are going up,I don’t understand.About week 8 of flower plants look great,tricomes about 50/50 white / clear.It looks to me like they stopped eating.Water going in is about 350 ppm could this be causing the problem.@Bulldognuts I saw you have an RO buddy how much water do you lose to get a gallon of RO water


Welcome back 59griff.

When’s the last time you changed your RO filters/membrane? What was the TDS the first few runs after changing them? 300-ish TDS seems high for an RO system operating correctly unless you’re adding minerals back in. The RO should be removing all TDS.


This whole statement.

You say stopped feeding, how were u feeding before? Full strength with water in between? Full strength daily? What was the runoff when you stopped feeding? And were u seeing burnt tips, thus u stopped feeding, like why’d u stop?

To be honest, u never mentiond a flush. A complete dirty dozen lineup includes the flushing agent if im not mistaken… have u flushed according to schedule?

Sidenote: those towers u call colas look AMAZING. Keep doing what ur doing. But asking helps. Push them ladies these last 4-5 weeks and ull be lookin at an outdoor yielding indoor harvest

1 Like

If you have the dirty dozen, you should have sledgehammer. Just run (I think it’s 2tbsp/ gallon) and run twice the amount of your normal watering through. Let it dry out and continue plain water until harvest.


@MH47 I don’t have an RO system I just read in a separate post a bulldog nuts did I had heard you have to go through about 5 gallons of waste water to get 1 gallon of ROwater I didn’t want to do that

@PurpNGold74 I have been feeding half strength for the last month I used sledgehammer when I was supposed toLast time about three weeks ago. I was planning on harvesting about now so I stopped feeding and just water the last 2 1/2 weeks to get the TDS numbers down to as close to zero as I could and then harvest The numbers just started going back up I don’t understand why the plants look healthy. Like they are still eating.I’m just trying to get my head around these TDS numbers if I’m going to be adjusting my nutrient level from them on my next grow

1 Like

@BobbyDigital I ran the sledgehammer a few days before the last time I fed then went to straight water after that.I skipped final flush this time I had seen a lot of people don’t do it just straight water the last two weeksI just don’t see how the numbers went down steady after my last feeding and then the last week and a half they started going back up when all I’m giving them is waterJust thought my 300 TDS water might be throwing my numbers off but still I thought I should be down below 1000 instead of at 2000

Ah. I stand corrected. I thought your RO system was producing 300+ TDS RO. :flushed: mea culpa.

Much like showering, washing clothes, and cleaning your dishes, your home’s water supply is the tool you use for these activities. In the process of completing these tasks, water will inevitably be spent.

Same for cleaning water with water. RO systems do produce waste water to produce clean RO water.

So you think controlling me dissolved solids could be a problem I’m creating myself with my bad water.If you have an RO system what type do you use

So lemme get this right.

Uve been feeding at half strength….

3 weeks ago, u felt as tho the harvest window was approaching. So u flushed (with sledgehammer) then have been all water since.

Ur ppms (tds) is rising tho?

So half strength what? The entire dirty dozen? What were ur ppms looking like going in? If u have to, mic up a batch ud normally feed with and get some readings.

After ur flush, how were the numbers?

And by rising how much?

Finally, what soil are u using. FF?

@PurpNGold74 feeding half strength of Fox farms recommended week 11 last feeding. Ppms were 3000 after the last feeding checking every couple of days after that with just water it went down to 2000,1900,1700,1600,800 then started going back up 1000,1700,2000 checked last night at 2500.Ph’d all the water out 6.3-6.6 all the way.FF happy frog soil.Plants are done I am getting ready to harvest. Trying to be more scientific about this and have the PH Ppm and the plant tell me how to control my nutrient level But this ppm levels are really messing with my head

1 Like

Sometimes they just do wonky stuff in the root area. This is honestly not like anything ive dealt with myself.

But maybe u have high salt patches in the soil that held a bit more ppms then the reading said. All in all, not a big problem. And not really a learning experience neither, most plants wont give u this kind of issue.

Anywho. Happy Harvests!

My last feeding was 1500 going in 3000 coming out than steadily down and started coming back up to now


@PurpNGold74 thanks for the input all turned out well in the end anyway👍

1 Like

No problem my guy. Best of luck with the next crop

Stupid question after seeing those amazing colas, but could they have wicked some run off back into the root zone, if they were sitting in pot saucers??

Good question,I don’t know.I wish someone could educate us both.They are in pot saucers

1 Like

I fill 3 and 5 gallon containers, I’ve never actually measured the waste output vs clean. I’d say it’s probably 4 waste for every 1 clean.

Not to bad ,Just a hose from the RO buddy into a container and one to drain

1 Like

Yep, I stick the waste line into drain, so I can’t see how much water I’m wasting :slightly_smiling_face::grin:

1 Like