Is this light stress/heat stress?

[Indoor55]

Thank you, u have helped me a lot. Good day🍁

[azorahai]

Sometimes it's hard to accurately identify the problem, but you can narrow it down significantly. You've already raised the lights, and I'd say your pH of 6.0 is mostly fine, so all that's left from what was suggested here is to up the nutes in your next watering and see if it stabilizes or not. The blemishes won't disappear, but they shouldn't grow.

[RetiredGuy]

Instead of watering with pH 6.5 water, increase the pH of your next watering to 7.0 to increase the runoff pH.

[Indoor55]

I don't have any product but i could buy one. Any recommendations?

[Rwise]

Thats on the low side, can you get it up to 6.3-6.5?

[Indoor55]

Also i have to say that leaves in the inside of the plant that are not exposed to light look healthy. This makes me think that maybe the problem is not pH/nutes... What do you think?

[Indoor55]

I moved up the light and all my plants have recovered except one, showing this symptoms. Anyone has seen them before? Thanks for your help!! ☘️

[Indoor55]

6.0 pH

[Rwise]

Not enuf info, whats the PH? Looks like lockout from here.

[Xena]

Definitely not heat stress since you seem to be pushing the too cold side. IDK for sure but I had light burn last go and it didn’t look like yours. Some of the spots look like what I see if I splashed nute water onto the leaves.

[azorahai]

Perhaps share more pictures from the whole plant and the areas affected. How often are you feeding it? Do you have a TDS meter to keep track of how many ppm is put in and runs off? It's not completely necessary, but it's nice to have. A very low run-off ppm after watering might be a sign that you should increase how often or how much you feed, for example. Alternatively, a very high run-off ppm might indicate you're close to or already over-feeding it, which could burn your plant and lock it out of nutrients in the substrate/soil.
There's always the possibility of a pH problem (possibly too low), which could hinder the plant's capability of absorbing some nutrients. Those cheap pH strips are helpful, but a pH meter is recommended.

[Indoor55]

Yes, but i tend to add small ammounts, so maybe i have to increase the dosis...
Some plants started bleaching on the tips of the branches, and leaves were down and dry. Also some leaf tips were burnt. Im certain that they have suffered light stress but, as you say, the symptoms in the pictures Dont look like light stress so i don't know

[azorahai]

In my experience, light burn begins with bleaching at the tips and sides of the upper growth (closer to the light source), and it looks very different from what I'm seeing in your plant. Where are these symptoms first showing? If it's in the lower leaves (older growth), it's probably potassium deficiency. Are you feeding it any nutrients?

[Indoor55]

My temp is around 20°C during the day and 14°C min. at night

[Xena]

What is your temp?