Yellow leaves on plants

Question

I have many plants in pots in my balcony. It is April, so nights are still rather chilly (7-9 deg) so usually I put my plants inside at night. I am not sure if connected but sometimes I leave them outside. Lately I have noticed that some of the leaves were turning yellowish, on the tomato, basil, bell pepper and raspberry. You can see the picture attached. It is consistent in several pots almost everything but the strawberries and the rhubarb.

I am not sure what am I doing wrong, I thought it was a nutrient deficiency so I bought and treated with the product in the picture attached, it could be that. It could also be the soil, as all pots have the same soil brand. Lastly I am not sure but water here is very hard I have notice it leaves calcium traces on the floor.

What could it be and how can I fix it.

Thanks for the help,
JG

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Answer 1

This actually looks more like sun scald to me. If the plants have been indoors, they should be slowly introduced into sunlight; morning sun and afternoon shade to start, then slowly work up to full sun (at least 6 hours).
Little seedlings will need more sun protection and will need to be hardened off for life outdoors.
Avoid splashing water onto leaves.

These articles will help you.
https://www.gardeningknowhow.com/plant-problems/environmental/leaf-scald-in-plants.htm
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/how-to-harden-off-your-seedlings.htm