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Since your nutrients are low, try feeding three times as much for a week and see what happens.

I've only heard of those crazing, not cracking.

Those strip lights don't crack but they go out a lot. At least they are cheap.

And even if the glass leaked, the lights won't short out because they are on a (usually) isolated power supply.

It would crack quicker.

I've heard of these cracking a lot. The expansion on the led side, and the contraction on the water side, stretch the glass.

I don't think so. A little rest usually always helps.

Make sure the power supply comes with the new lights. Or make sure the current power supply can handle 5 watts.

Get 660nm reds.

Almost certainly it's the weak light compared to the low nutrients. If it's really 2 watts, and it's 3000k which has little red, then that little bit of red light stretched along the long tube will...