Need advice on runoff numbers

It’s a bit of both.

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Most nutrients will lower the pH, but not all. Letting water sit will also cause the pH to drift. That’s why we test pH just before watering/feeding.

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As mentioned above, your numbers from month old ffof seem atypical. The low ppm might be from the added perlite, I suppose 25% might also prevent the soil from buffering as it normally would.

To be sure, I’d do a slurry test or two from different areas of the pot.

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@smokysmurf what is the frequency at which you are testing your runoff? An example are you testing when the saucer is first full, or are you testing after like around the fourth?

This was my first watering to runoff, so first test. I will be starting nutrients with the next watering so I am interested to see what my runoff is. I am in a 5 gal Smart Pot and had approximately 1/4 of a liter of runoff. Is that about right or should I have more runoff?

@MidwestGuy @Myfriendis410 @TheAccused @Arborfarms @Drinkslinger I just did my second watering to runoff. This was using Big Bloom at 25% dose. My TDS is 2130. My runoff PH is still too low at 5.6. @dbrn32 recommended adding some lime to the top of the soil. FixerPower suggested watering with 7.3PH. The problem is after adding the Big Bloom my water PH was at 7.7. I tried to add the tiniest amount possible of PH down but it still brought it all the way down to 6.5.

Would it hurt to water next time with 7.7 PH or should I just go with the lime?

I was hoping my runoff PH would come up to the normal range at the second watering to runoff but it obviously isn’t going to. Thanks guys.

I just did some calculations and if I used 7.7 PH water and my runoff is currently 5.6 that would come out to a potential runoff of 6.65. 7.7 + 5.6 = 13.3/2 = 6.65. I think this is the correct theory?

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Much better to use the lime. You can’t really do too much with water to adjust media and it’s unwise to deliver out of range the other way. If you do that do not exceed the maximum range for your media. If soil that would be 6.8.

This is a pretty complicated formula as you have to factor in the density of the two media.

Was this runoff or input?

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What he said :point_up::point_up::point_up:

TDS was runoff.


Dolomite Lime Plus Magnesium and Calcium"Greenway Biotech Brand" 1 Pound

Dolomite Lime Plus Magnesium and Calcium"Greenway Biotech Brand" 1 Pound

Would this be a good choice since I am not using calmag?

This is due to CO2 venting out of the water, reducing it’s acidity. Also; testing any water under 100 ppm is unreliable. Both for PH and TDS.

I think this is acceptable and no supplements needed until runoff drops below 2,000 ppm in soil.

I prefer straight dolomite lime (powdered). You’re just looking to buffer pH at this point. This will also add calcium.

Also, that’s mighty expensive. I pay about $5 for 50lbs of dolomite lime at my local gardening shop. I also pay about $4 for 5lbs of Epsom salt (which adds magnesium and sulphur ).

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In all honesty you are better off not worrying about what your outflow pH is, you are going to be chasing your tail.

Some advice for the future, auto’s are best grown in Coco imop. Your soil composition is based off slow release nutrients, and with the rate at how fast auto’s grow the soil she is in is going to be of little benefit. If she was a photo she has all the time in the world to take advantage of those nutrients.

So if you use fox farm ocean forest there’s no need to use any fertilizer until they start bud?

It depends. I’ve had FF Happy Frog (less hot than Ocean Forest) last 8 or 9 weeks, and I’ve had it last only 4 weeks. It depends on the progression of your plant. The only reliable way to monitor what is going on in your soil is to monitor PPM and begin feeding at PPM < ~1,000.

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Thanks! Great info…

@Drinkslinger @Myfriendis410 @MidwestGuy @TheAccused @Arborfarms @Wowzer @dbrn32
I watered again today and my runoff PH is still 5.5. Any ideas on why my runoff is being so stubborn? This is the second time I have watered since adding dolomite lime. I know some of you are saying not to worry about runoff PH but I am concerned my plant may be missing out on some nutrient uptake due to the low runoff PH.

My TDS had gone up to 3440. Does this indicate I should water with plain PH’ed water next time?

I am still using Big Bloom and Tiger Bloom at roughly 25% strength.

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Your last runoff was 2100± and the current one in 3400±? I’d say just water next time for sure.

What was the pH of the nute solution before adding it ?

At 3,400 ppm I’d flush and reset. This may also bump your PH up.

Yeah, I was surprised by the jump in TDS too.

The PH of my water with nutrients was exactly 6.5. I calibrate my PH tester every time I use it.