The poor through test .

[Undergrounder]

The pour-thru test they mention in that article seems wrong... they mention that 2 gallons of water should be poured through the medium and then tested. And this solution is supposed to have an EC between 1 and 2.5 just from the runoff alone?

Why 2 gallons? isn't that a bit arbitrary? Wouldn't it also depend on the size of the pot what the final EC value is? If you put 2 gallons through a 50mm seedling pot you're going to get a smaller EC than putting 2 gallons through a 300mm tub.

I would use one of the more scientific methods i linked.

[Masdyman]

I have done further tests with less pour through water 2oz and the results are now 200us in CHC PH 6.5.
I also tested it through a orchid in moss which was 200us PH 3.7 ! So this orchid is in a medium which is too acid and possibly limiting certain elements so is in need of a re pot .
My orchids have only been in the husk since March some less ,could this be the reason the EC is alot lower than the 620us solution .I pour a lot of feed solution when i water so know this isn't the reason .

[Hedge]

Basic ignorance being demonstrated here: what are the units you are measuring electrical conductivity in, and what do you use to measure it with? I have a basic volt/amp meter but nothing else.

[Masdyman]

Originally Posted by Undergrounder

The pour-thru test they mention in that article seems wrong... they mention that 2 gallons of water should be poured through the medium and then tested. And this solution is supposed to have an EC between 1 and 2.5 just from the runoff alone?

Why 2 gallons? isn't that a bit arbitrary? Wouldn't it also depend on the size of the pot what the final EC value is? If you put 2 gallons through a 50mm seedling pot you're going to get a smaller EC than putting 2 gallons through a 300mm tub.

I would use one of the more scientific methods i linked.

Hello I don't know what part you read but it states pour enough water through the pot to collect only 2 oz,so it isn't much at all .

[Masdyman]

Originally Posted by Hedge

Basic ignorance being demonstrated here: what are the units you are measuring electrical conductivity in, and what do you use to measure it with? I have a basic volt/amp meter but nothing else.

I have a EC pen which measures in Microsiemens(ms/cm or us/cm).It also measures in PPM but this is only a conversion from ms/cm so isn't as accurate .I also have a PH pen ,both of these i purchased through Ebay Ph pen £15 - £20 and the EC pen £24.99 .

[Ray]

Don't put much faith in the RO water being at a pH of 6.5. It is only acidic because of the absorption of carbon dioxide from the air and the subsequent formation of carbonic acid. Fortunately, carbonic acid so such a weak acid that it is overwhelmed by almost anything.

So, if you're seeing a pour-through pH of 6.5, do not interpret that as the medium playing no role in adjusting it, but rather than the medium is lowering it from 7 to 6.5.

[Masdyman]

Originally Posted by Ray

Don't put much faith in the RO water being at a pH of 6.5. It is only acidic because of the absorption of carbon dioxide from the air and the subsequent formation of carbonic acid. Fortunately, carbonic acid so such a weak acid that it is overwhelmed by almost anything.

So, if you're seeing a pour-through pH of 6.5, do not interpret that as the medium playing no role in adjusting it, but rather than the medium is lowering it from 7 to 6.5.

That what i thought , i have about 10 l of RO in a tub whilst i have been doing these tests and the RO is now 6.5 ph i thought at the time it seems lower than normal so i tested my ph pen which was accurate .So i cannot explain why my RO is 6.5 .Does it drop the longer it is stored ?

[orchids3]

Have not read your article yet but thanks for posting the reference - will read it gladly.
I have often checked the pH of my potting media by (1) placing the whole pot in a pail of distilled water and soaking if for an hour. (2) lifting the whole pot out quickly and let the pot drain into a second pail or pan. (3) check the drain out water for pH. I think you would get a good check of the EC as well. Seems to me it would give a more accurate reading of the conditions inside the pot than pouring water thru. Of course I doubt you would do a big collection this way but rather a spot check around the collection periodically.

[Ray]

Originally Posted by Masdyman

That what i thought , i have about 10 l of RO in a tub whilst i have been doing these tests and the RO is now 6.5 ph i thought at the time it seems lower than normal so i tested my ph pen which was accurate .So i cannot explain why my RO is 6.5 .Does it drop the longer it is stored ?

The pH is lower than 7 - the true pH of 100% pure water - because it has absorbed carbon dioxide from the air and formed carbonic acid, H2CO3, which, when ionized in solution, lowers the pH.

Can it go lower? I suppose that depends on your air quality and the dissociation constant of H2CO3 - and I cannot give a good answer, with my lack of knowledge on the specifics.

No matter what, it's nothing to be concerned with.