Reducing lighting time.

b4tn · May 3, 2019

My scrubber is stripping all nutrients from the water and actually working to well. I reduced the lighting period from 14 hours to 12 hours and a week later I am still not really seeing nitrates come up. I just reduced lighting period again to 10 hours and will test again in a week. What would be the minimum lighting period before I need to find other ways to get nutrients up? The intensity is at the 3:00 position The scrubber is almost 4 years old.

Turbo's Aquatics · May 3, 2019

There are a few things to consider.

Intensity is really the primary value that affects nutrient levels. Varying the duration at a given intensity is more of a secondary level of controlling the overall level of filtration.

If you break down photosynthesis to a basic level, the energy of X photons is used to convert Y amount of nutrients into Z amount of algae. Intensity is the rate of photons, and is an "instantaneous" factor. Your water flow (and nutrient levels) determines the rate of Y nutrients delivered to the algae. So if you crank up on X (intensity), you'll suck out more nutrients faster. If you vary the duration, you're still maintaining that rate, just for a different amount of time.

Some of the older information is along the lines of "higher intensity and lower hours is better than lower intensity and longer hours". But, that really was in relation to CFL and T5HOs. These rules do not apply to LEDs, and not all LED fixtures are the same.

I had my lights tested on a high-end spectrometer for both spectrum and intensity at various dimming points. When you are running the LEDs at the halfway point on the intensity, then go to the 3/4 point, the intensity doubles. Going to full power doubles that again.

So I am now referring to the halfway point as 25% power, 3/4 point as 50% power, and then of course full=100%. I had a few other random fixtures tested also, and to make a long story short, I didn't find a similar (physical) size fixture, running at 100%, that exceeded the intensity of my fixtures when they were set at 25%. And on top of that, that intensity at 25% is at least equal to, if not higher than, what you would get running a high-intensity CFL scrubber.

What this basically means is that everything you read about running lights at full power 24/7 - the equivalent of doing that with my fixtures would mean setting them at 25% for 24/7.

This is a really long dissertation to basically say, lower the intensity (first) and run longer hours (maybe). So I would dial it back to about halfway between the 25% and 50% point (call it 38% lol), and leave the hours at 10 and monitor for a while. If you find a point where your nutrients are starting to creep up, then add hours. You can keep adding hours until you're at 24/7, if needed. Then, if you see nutrients creeping up again, bump the intensity back up.

I suspect you will find a sweet spot at that 35-40% level and about 14 or so hrs/day...just a hunch

b4tn · May 3, 2019

Thanks for the detailed response that’s a big help. The dial is a bit odd. Would you say 25% is around the 5 o’clock position and 50% at 3?

Turbo's Aquatics · May 4, 2019

The pointer straight down is 25%. Straight up (fully turned to the stop point) is 100%, halfway between is 50%.

I switched from a left-turn to a right-turn potentiometer in January. So I’m trying to describe this in a generic way from now on in order to avoid confusion.

b4tn · Dec 15, 2019

I am finally at a point to where I feel like I can adjust my nutrients by turning a dial

. With my current feeding schedule I had my scrubber set about 30 percent on the light dial for 10 hours reverse light cycle. It sat like this for several weeks and N and P hovered around 4/.08. I turned the dial up closer to 50%, waited a week and N and P went to 1/.04. I did my weekly water change today and dropped the intensity down to about 40% to see if I can get a tad more nutrients and will most likely stay there but will check again next week. I expect to get somewhere around somewhere between the two values.