Advise for light duration for MH

[o2bubble]

Hi all, I intend to use 2x150w MH lights for my 4x1.5x2 tank with mainly fast growing stem plants. I saw ADA’s recommendation to use only 6-8 hours max with MH and Dennerle recommends the on-off lighting method to reduce algae.

There are 2 options which I’m considering and hoping for advice:

• Continously 6 hours per day

• On 3 hours, off 3 hours and then on 4 hours again (total 7 hours)

[valice]

The rationale of ADA using 6-8hours only is because Grand Solar comes will two tubes of PL. Therefore, the rest of the 2-4 hours are lit up using the PL lights. Sort of a morning/dusk effect?

And, I believe you are merely using 2 pieces of MH lights. So maybe you want to alternate the lighting to achieve a continuous lighting period of 10hours. That's one short-coming of using purely MH lights.

There are many debates on the effectiveness of siesta on algae growth. Some say it is useful, some swear that it is useless. So maybe want to trial and error on this to see if it is effective for you.