Possible the bulb is too strong/near the screen, for the amount of flow it has. When flow is weak, the wattage has to be reduced from the recommended amount, or, the bulb distance needs to be increased.I am finding that the lower half of the screen which is not so brightly lit is getting more growth on it than the screen which is directly under the lights?
Only if they did the verticals wrong. When done correctly, especially with strong light and a rough screen (like mine) they can be full in 7 days from a brand new screen (like mine was two weeks ago when I converted to a roughed up double layer.) Most of the "delayed" ones you see are because of smooth screens, and weak light. Only last month was it realized how critical a super-rough screen is. I don't criticize theirs too much if they are on a different forum from here, though. Here, however, I do need to point the what is known to be correct.horizontals seem to get started so much quicker them verticals as there are many posts from vertical users who see no growth after weeks
Yours is indeed having a good start, congrats. And not to sound negative here, just realistic (and experienced). The growth you show is really not massive, it's average. I know it feels great, but remember I've watch hundreds of scrubbers develop from day 1 to one year. When they have rapid flow, strong light, and a rough screen, growth is incredible (i.e., your screen would be 1" thick in GHA by now, and need cleaning). My viewpoint is really not for you, though, so much as it is for readers who are trying to figure out what to build. They just need to know the good and bad to all options.Yes massive growth and can see the difference overnight.
Because there is no growth yet. When (if) the GHA gets to 1" thick, or even 1/2", that's when flows get stopped. The trick with yours will be to clean before this happens because the algae further down from this will die. I don't think it will get that thick, however, because of the lower flow, and the smaller bulbs that you said you might try.No Blocking of flow