I've never heard of PVC expelling that amount of acidity. To correct pH immediately, I would add a small amount of hydrated lime. The hydrated lime reacts almost instantly and should be used in small amounts when container gardening. Use dolomitic lime to correct pH over longer periods. There are many useful websites to find the correct amount of lime to use, according to the volume of your "soil." Know this, highly organic soils can be effective mediums at a lower pH than mineral soils. If your planters are mostly peat they can support most plants at pH >5.5 without aluminum toxicity. Mineral soils require a higher pH, somewhere between 6 and 7. Know what type of soil you have and add enough lime to raise to a pH of 6.5. If you keep losing plants after this you have other problems. Good luck.

M

Some hydroponic farmers locally use PVC gutters for growing. A do not think PVC is the problem, I am also doubtful about PH being the cause. Using the mix you are using I do not think works for long time growing. I do not think it will hold up for the length of time you have been using it. Al

I measured pH and to my surprise I found that pH was more than acid. My instrument measures from 3 to 8 and the measurement was off scale on the acid site.

What instrument are you using to measure ph? If your ph was 'off the scale' and your instrument measures as low as 3 then your instrument is simply giving a false reading.

You would need to water with sulfuric acid to get it lower than that ;-)

I suspect ph is not what killed your plants.

Store bought pH meters are notoriously incorrect.

My pH meter is build by Kel Instruments and is called Kelway.
I have measured other soils, in pots and in my garden and they all measure what I think correct, between 5 and 7. My garden soil measures around 6.7 and pots of Hydrangers are indicating 5. The color of the flowers are light blue. I will add a bit of sulfure to make the flower a bit more blue. My Anthuriums are growing fine and they measure about 5.
I changed the potting mix to a new one and that now measures 6.5. Next week I will plant new plants, lets see what happens.
Thanks a lot for all your kind answers. A merry Christmas and Happy New Year for all of you.

It may be difficult to believe that rain can have such acidity that it may be the cause of your reading.
A few years ago, there was a number of articles written in newspapers and magazines about how acid rain is destroying the lakes and rivers in the north-east U.S. and in Canada.

In such a small volume of soil, I don't believe adding lime is a wise choice. It can change soil so drastically if one does not know just how much should be given.
Even a soil test may have difficulty giving such a measure for such a small amount of soil with a reading of much acidity.

I think if Pogon, you change some parts of your treatments you may find the cause.
It is suggested by the others that the PVC is --should -
not be the cause of such acidity. To that I have no idea,
but, you could change it to a different material.

Acid rain. I don't know that either but acid rain IS a constant that could be looked at.
A call to your local extension service asking them if acid rain in that part of the country is a factor that might change such low volume of soil.

You didn't mention about how well your containers drained.
THAT could definitely cause such problem to plants that would end up in their death so quickly.
Then too, if they do have drainage holes, are they protected from being plugged with soil.
Containers are commonly given something between the holes and the soil so that the box can drain properly.

Sulfur is not the element that contributes to the blue color of hydrangeas, but aluminum. In situ plantings of hydranges can be 'blued' by adding sulfur, but only because of the resultant drop in pH which releases tightly bound aluminum ions from the tight grasp of soil particles. For containers, your plants would be better served by adding aluminum sulfate as you water the plant.

Cutting back on phosphorus in the fertilizer can also help.

Yes, my container has a lot of holes and water flows right through the potting media. The container is a window box so it does not contact the ground. My soil pH below the box is 6.5
Thanks for your help. Season Greatings