Blueberry plants seem to be dying

[Daytosan]

Hi,
I have 2 blueberry plants growing in pots. Or "growing"...
1 is having increasingly more & more darkening leaves.
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My second blueberry plant was smaller, and had the same or a very similar problem, before losing all of its leaves. Now it just looks like this, and has done for the last month.

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What do you think is wrong with them ?
They are getting sufficient water. They may actually be getting too much... They are in direct sunlight for about 8 hours a day. I try not to water over the leaves, but directly at the base of the "bush".
Any advice, input, would be much appreciated.. Thank you !

 

[Susan BBPM]

Unfortunately I can't view the images. But what you describe could fit with a problem we've had.

We had a problem with our blueberry bushes. We potted up 5 of them, but left the three that were potted up last year. We did sprinkle sulphur chips on the surface along with slow release fertilizer.

The leaves on the 3 that were potted up last year started to go red and some fell off.
One of the causes of this is soil too alkaline. We did a test and sure enough, the recently potted up were fine, but the three from last year (that were looking unhealthy) were neutral.

No point adding sulphur chips at this stage as they won't work in time. I have no clue if this was a sensible thing to do, but we put some vinegar in with water to try and temporarily lower the ph. It does seem to be working - we've done it a few times now and the ph has lowered. We plan to repot in winter with more acidic compost.