Testing pH by soil runoff?

How accurate of a pH indicator is taking a soil runoff sample? I am growing in soil and I need to find out the pH so I can solve a problem.

Some of my fan leaves yellow a little too fast during flowering, by the end of flowering sometimes I end up with no fan leaves, the plants suck nutrients from them in succession - moving from oldest lower fan leaves to topmost fan leaves; they die off 1 after the other its crazy. I know this is normal in flower but not starting in the first or second week!?

So I know I'm guessing I am experiencing one of two problems.

1) Flowering solution does not deliver enough N to keep fan leaves alive. The plant needs to use the N from fan leaves as a source.

2) My pH is screwed up and the nutrients I'm giving the plants are being locked out. The problem with this theory is that in soil at 5.8-6.2 like mine will not lock out N. But will lock out Ca and Mg.

Here is my grow Data

Flowering Nutrient solution

• NPK ratio: 9-16-21
• pH of solution mixed in 7.0ph Water: 6.2
• Average pH between 6 plants = 5.5 (This is only as accurate as testing soil runoff.)

The last time I fed them was 1 week ago (11/16/2009). Since then I have watered them with plain tap water 2 times at 7.0pH. I left the water sitting out a for a few days to evaporate the calcium etc...Today I used regular tap water again until a little runoff came through the bottom. I collected it and used one of those pH test kit droppers.

Lets just say my soil pH is really around 5.5 after two plain waterings. Will more and more plain waterings finally raise the pH?

Thanks for the help, sorry im pretty baked so I may have just kept rambling haha you know how it is

i would have to think so im relying on that to help as well my ph had dropped to destructive levels killing one plant and severely damaging another all because i didnt know that certain nutes drop your water ph drastically to the 3.0 levals i did adjust mine with ph up over the last week and a half and im doing fine now good luck with your grow...peace pot prosperity

stinkbudd1 said:

i would have to think so im relying on that to help as well my ph had dropped to destructive levels killing one plant and severely damaging another all because i didnt know that certain nutes drop your water ph drastically to the 3.0 levals i did adjust mine with ph up over the last week and a half and im doing fine now good luck with your grow...peace pot prosperity

Click to expand...

Heh that is another question I had. Could you just add pH up to the solution to raise it to your desired level? Will that mess up your nutrient ratio? Can you raise the pH and still maintain the same NPK ratio?

I read this from http://www.elmhurst.edu/~chm/vchembook/184ph.html

Pure water is neutral. But when chemicals are mixed with water, the mixture can become either acidic or basic.

Click to expand...

So the mixture of chemicals is what is making a feeding solution acidic. If you add pH up what is happening in chemical terms? It has to mess up the NPK ratio right? I dunno lol.

im not sure about the chemistry side of it but the way i do mine is to mix my nute cocktail and then take its ph if it is low as i now know ity will be i ph it up i always ph it up to at least 7.0 ive not had problems since i started this and if i go in and take first run off of my plant and test it now im useually right around 6.0-6.6 so thats fine with me..i hope this helps you some...

stinkbudd1 said:

im not sure about the chemistry side of it but the way i do mine is to mix my nute cocktail and then take its ph if it is low as i now know ity will be i ph it up i always ph it up to at least 7.0 ive not had problems since i started this and if i go in and take first run off of my plant and test it now im useually right around 6.0-6.6 so thats fine with me..i hope this helps you some...

Click to expand...

Yeah that definitely helps! I appreciate it. I'm going to get some pH up tomorrow so I can start pHing my water. I'll let you know how it turns out

Ive got a runoff pH of 5.5 as well i water with pH 6.5.
plants are looking good
may try to raise my run off.

basically because if your watering with 6.5 and your run off is 5.5 this means your soil pH will be around 4.5 - 5.0 as your soil will be compensated by the higher ph of the water

to me this seems low what do u think

I was having the same issues.
I have solved it by adding dolomite lime 1tsp per gallon of soil.
During the third weak of flower.
Ad a ?
Did you say you are water water feeding.
What soil are you using?

Lets first look at y ur buds look so fluffy... U might be having a heat issue

bossman88188 said:

I was having the same issues.
I have solved it by adding dolomite lime 1tsp per gallon of soil.
During the third weak of flower.
Ad a ?
Did you say you are water water feeding.
What soil are you using?

Click to expand...

Yes I am watering 2 times per every feeding. The soil I'm using has no fertilizer in it, and the brand is Fafard.

SunnyD said:

Lets first look at y ur buds look so fluffy... U might be having a heat issue

Click to expand...

With that particular grow in the picture I was using CFL and yes it did get hot in there when it was closed at times. I'm growing the same strain under a 400w and its still pretty airy, it was bagseed so it is just crappy genetics.

IMO with a nute less soil.
I have alway's been told and done a feed'feed'water.

I did a test today to find out the pH of the soil. I ran some 7.0 water through fresh soil from the bag and the runoff came out to 5.3 pH. I don't see how this could be but the test was fairly simple. Water at 7.0 pH. Soil in a plastic cup with holes in the bottom. Ran water through it for a little then collected a sample - 5.3. Tested it again, and again and again and same result. If the water is 7.0 and runoff is 5.3 what is the actual pH of the soil?

bossman88188 said:

IMO with a nute less soil.
I have alway's been told and done a feed'feed'water.

Click to expand...

The instructions said water,water,feed but I'm sure they're playing it safe there. I was thinking of doing a water,feed,molasses watering schedule. Problem is I want to pH my feeding / molasses solutions before I feed and lower the damn soil pH further.

I use sunshine mix #4. The PH is also very low to start.
So I flush it very thoroughly with RO water. To balance it out.

bossman88188 said:

I use sunshine mix #4. The PH is also very low to start.
So I flush it very thoroughly with RO water. To balance it out.

Click to expand...

Sounds good man. Thanks for the help. I'll let ya know how it turns out with some pics