Advise on plants turning yellow and black

[baranne]

Need some advise guys.

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I've been seeing my plants turning either yellow for the nanas and black for my carpet (I believe I have a mix of MC/HC).

What kind of deficiency could this be? Reading online I couldn't determine if it's nitrogen, phosphorus or iron deficiency. Or even excess phosphorus.

Light is 55W on total of 6 hours daily (3 on morning, another 3 on evening), 2ft x 1ft tank (60l), CO2 checker green. I've stopped liquid ferts for now, was dosing flourish potassium and micro traces per instructions. Plants bubbling.

Thanks in advance!

[baranne]

To add on, light is PL.

I also see the roots of my dwarf water lettuce turning black:

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[Shadow]

Light deficiency, do not ON the light less than 3hrs per session. It killing the plant, some plant might be more tolerant but in my experience most stem plant will die.

[baranne]

What's the minimum hours I should have them on at one time? I prefer to have them on once in the morning and once at night if possible.

[baranne]

Sorry you said 3 minimum. Ok I'll go with 4 each time and try it out. Any other things to think about?

[Shadow]

my mistake, minimum is 4 hrs per session

[baranne]

Thanks shadow