pH and EC meter problem

[Ray]

Watered today with 600 µS (only calcium nitrate). Waited 2 hours after watering, then used RO water and collected about 50-100ml at the bottom. EC of my RO water: 30 µS. EC from collected water: 90 µS.

What am I doing wrong? Waited too long?

The pour-through test was designed to allow the determination of the substrate pH, not the EC.

Basically, you have simply demonstrated that your plant and potting medium absorb the nutrients, which isn’t very valuable information. Did you wait too long? Who knows, but I’d bet your pour-through EC would have been higher had you not waited so long. Did you trickle the RO uniformly over the entire surface, or did a bunch get dumped over a smaller area? That’ll effect the results, as well.

 

[katzenhai2]

The pour-through test was designed to allow the determination of the substrate pH, not the EC.

Basically, you have simply demonstrated that your plant and potting medium absorb the nutrients, which isn’t very valuable information. Did you wait too long? Who knows, but I’d bet your pour-through EC would have been higher had you not waited so long. Did you trickle the RO uniformly over the entire surface, or did a bunch get dumped over a smaller area? That’ll effect the results, as well.

I had the impression you suggested that terryros' idea of measuring the EC in this way wouldn't be wrong.

I watered slowly and over the entire surface of the pot.

I fear the following: If the substrate never dries it will never absorb new water and its components?! Then the new water would just flow through from above without any effect. It would only be absorbed by the roots the moment it hits them, for a very short period of time. Maybe thats a naive thought.

I also measured the pH: The collected water from a newly repotted plant was 6.8. With a (not so long ago) limed one it was 8.1. But since the water only had 70µS and 90 µS respectively, this measurement is too inaccurate anyway. That's why I measure the EC and it is too low for a reliable pH measurement. Thats my main problem. Maybe 500 ml is not enough? How much water flows through your pots on average when watering?

 

[terryros]

The correct amount of fertilizer depends on a number of things including temperature, amount of light, type of orchid, potting media, and number of healthy roots. You might be doing it just right.

 

[Ray]

I had the impression you suggested that terryros' idea of measuring the EC in this way wouldn't be wrong.

I watered slowly and over the entire surface of the pot.

I fear the following: If the substrate never dries it will never absorb new water and its components?! Then the new water would just flow through from above without any effect. It would only be absorbed by the roots the moment it hits them, for a very short period of time. Maybe thats a naive thought.

I also measured the pH: The collected water from a newly repotted plant was 6.8. With a (not so long ago) limed one it was 8.1. But since the water only had 70µS and 90 µS respectively, this measurement is too inaccurate anyway. That's why I measure the EC and it is too low for a reliable pH measurement. Thats my main problem. Maybe 500 ml is not enough? How much water flows through your pots on average when watering?

Certainly testing the EC tells you something, but I question what, how much, and what is the value of it?

Potting media staying wet does not mean they stay 100% saturated at all times; they all lose water, so are, indeed, rewetted with fresh solutions. How much is yet another unknown...

As I have plants in 10" pots and others in 2" pots, I cannot give a reasonable estimate, but I speculate that it is well into the 1 or 2 times the pot volume range, as I typically use 30-40 lites when I feed my couple dozen plants from a hose-end sprayer, and flood them even more when it's just water from the hose.

The correct amount of fertilizer depends on a number of things including temperature, amount of light, type of orchid, potting media, and number of healthy roots. You might be doing it just right.

Bingo! There are a LOT of variables, so comparing your technique with those of others can be very much "apples and oranges".