nobody said they bought it because its a magical horticulture spectrum, they bought it because it produces results and is a well built product.
Mine is 7".It's recommended 1 foot to 2 foot off the waters surface depended on your fuge size
Another large factor in it is how deep your fuge is. Mine is pretty deep and I keep my light about 10 inches off the water surface, and my chaeto almost never floats to the top it sits on the bottom. But in all honesty, who wouldn't take a corvette though! lol
It's been my experience that the Kessil H380 matched with chaeto was able to reduce both phosphates and nitrates. Using GFO with chaeto almost always kills out the chaeto unless your system is extremely nutrient rich.
I have both. the h80 is decent for a small refugium but it is basically not a value when you consider the light output vs cost. I bought it with a specific use and it worked fine but this is a case where I would explore other options that would probably yield better results for less money especially if your fuge is >5 gallons.
I think there are other factors that come into play. Phosphate will reduce with better algae growth, which a good light can contribute, but also how much macro you have, and the type of macro as well. Carbon dosing can play a factor as well. Personally I don't use gfo at all in any of my three systems. I don't do water changes either. In fact in one tank I add liquid phosphate daily to keep it detectable. But it's all about system design as a whole. The kessil isn't going to make or break a phosphate situation alone.
