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What may cause my lettuce leaves to look like in these pictures?

I don't find any literature in my language (Bahasa Indonesia) that explain this phenomenon or find any similar images on the internet. The room temperature is about 25 degrees Celcius and the relative humidity around 55 - 65% during cultivation. The light was 24 hours straight.

I actually have two hydroponic systems that have the same lighting system. The first one I planted with lettuce that I planted on 7 September 2020 and the second one was on 3 September 2020. The picture I post was the lettuce that planted on 3 September 2020.

I don't find any problems with the younger lettuce. Their leaves are fine. But the older ones all look like in these pictures.

I thought its variety not suitable for these growing conditions, but I don't really know the variety because it's in Korean, but my supervisor called it "Bun". I attached the seed pack if you want to know. I have planted red rapid lettuce and also get this condition, but not as worse as Bun variety. Other lettuce have different problem but let's not focus on that.

I thought the lettuce bolts because they get 24 hours of light. One of the reasons for lettuce bolts because of the light duration not suitable for growth. Or because there is sometimes the water system not work well and causes the root system dry.

Can anyone shed any light on whether my assumptions are correct or not, and is there any way to not make my plant turned like this again?

The lettuce variety enter image description here

Bun Lettuce with white LED light Lettuce with white LED light1 Lettuce with white  LED light2

Bun Lettuce in White LED light enter image description here

Bun Lettuce in Grow Light enter image description here

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  • Lettuce is a cool climate plant. The ideal temperature range is 15-20C (60-70F) not 25. – alephzero Sep 29 '20 at 2:50
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That looks like tip burn, meaning that the foliage is absorbing too much light and heat and getting burned.

One thing is that grow lights should be on a maximum of 14-18 hours particularly during that stage. source Think about nature: there's never a period where there's 24 hours of sunlight (except in the arctic circle for a few weeks of the year). The darkness is the period during which plants metabolize the hydroponic nutrients you're feeding them.

As mentioned in the comment above, lettuce prefers a temperature around 15-20C.

The burned leaves won't recover, but you can prune them away and reduce the light intensity and time and the new growth might be healthy and avoid tip burn.

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