Hours Vs Intensity.....


Lifetime Members
Lifetime Member
Apr 24, 2015
Hello, hoping for some advice...

I have a 210g partially high tech (dropping pH 0.5) planted setup (avoiding hard to grow plants and don't want to do a lot of trimming).

Using this LED lighting setup: https://www.ebay.com/itm/3PCS-Fresh...-36-60-Tropical-Fish-Plant-Tank-/332619504046

Always had slighted green tinted water and it makes me crazy. I'm addressing all other potential factors, i.e. cleaning filters, water changes, appropriate sized feedings, etc....but want to eliminate lighting as the issue, as much as possible.

The tank sits near a window and get's indirect sunlight (not much I can do about that). The tank is 30" deep, so I feel compelled to turn the lights up to 100% in order to get the necessary par to the foreground plants.

My process has been: Lights at 20% from 1p-5p (4hrs) for some light and general viewing and 100% from 5-9p (4hrs) for aesthetics and provide adequate light for foreground.

If I want to cut the light back, in order to eliminate green water, what is the shortest light cycle you would recommend? Thinking of doing 5hrs at 100% and that's it?

.......and as Im typing this, thinking that there are so many factors to the equation, I probably just need to experiment?

Thanks for any help

Tim Harrison

Lifetime Member
Lifetime Member
Jul 7, 2017
I suppose it depends on what your carpet plant is. But good CO2 implementation is probably key to success. You can lower a plants light compensation point by optimising CO2 flow and distribution. But overall many folk make the mistake of using far too much light, especially when first starting out. I use moderate light intensity for just 6 hours a day with a short ramp up and down and have grown a variety of carpets including HC Cuba. But you are right, perhaps the best way is to experiment and watch your plants health. It you're methodical you'll find the sweet spot eventually.



Super Moderator
Staff member
Lifetime Member
Jun 20, 2016
Directly answering your question, yes 6h also works for me with 100+ species. If conditions are good you may get extra coloration / growth for the extra hours but for low maintenance mode, 6h is a good point.

The indirect sunlight is a troubling factor. If enough sunlight reaches the plants, it will start them up. Make sure the CO2 is at good levels at that point. You can put some cardboard sheets next to the aquarium to stop the sunlight reaching it. If green water persists, a quick cheat that works every time is to use a suitable UV for your filter.