quesion about my red mangroves

[mattyparsons]

i've currently got a 20 gallon long underneath my main display tank, which acts as a sump/refuge. i have hung a 65 watt 10k daylight powercompact above it for lighting. the lighting is on from around 8am - 8pm.

in the tank is planted 10 red mangroves which have been thriving and adding new leaves about once every 6 weeks or so. the tank is also packed with chaeto.

now that i'm adding more critters to the top tank, my plants are starting to have a hard time keeping the ph above 8.0.

what i'd like to know is how the mangroves would react to a 24 hour light cycle?

or maybe to a 20 hour light with 4 hour dark would be better?

anyone have any thoughts?

thanks in advance!

here's a pic -