Algae scrubber not getting the growth I expected

Sorry I meant to reply to these previous messages so thanks for updating the thread

Usually, once you get the screen to fill in, you can remove the diffuser and it should remain filled in. Usually.

I wouldn't think you would need a larger unit or stronger lights, if you've been running that for a year with 16 on / 8 off and diffusers in place, you have a lot of headroom to play with. You've removed the diffuser, so that is a major change. Adding hours is another.

Let it grow longer - more time. As long as the lights are intense enough (yours are) to penetrate through the algae mat (which isn't that thick, so light getting blocked and not making it to the base or the screen is not an issue) then you don't "need" to harvest.

Also, think "harvest" and not "clean". I would like to see one of your post-cleaning pics. You may be over-cleaning...which is why I've started to use "harvest". You want to leave a pretty decent amount of growth behind. One of the common misconceptions is that you want to fully remove all growth, and this really isn't necessarily true. You want to remove somewhere in the range of 75%.

You may also consider doing intermediate harvests, where you take the screen out, rinse it and rub it with your fingertips to remove maybe up to 50% of the growth (a light scraping might be done, but in strips in an "X" pattern or "#" pattern) and then put it back in. The idea here is to just "prune" and then allow a fast recovery. This is especially helpful when you are dealing with long-term high nutrients, but you have a somewhat mature screen. This is sort of your situation.

I think all you need to do is adjust your harvest method & frequency and then get aggressive with the lighting intensity and duration.

So

1) don't over-harvest or over-clean
2) this allows your screen to be able to handle the higher intensity light
3) do only intermediate harvests every 7-10 days, maybe even 14 - don't do a "full" harvest for a couple of months.
4) you've already increased intensity; so hold the hours and focus on doing #1 and #3
5) you should start to see the growth bulk up a bit, and nutrients should start to drop.
6) as long as #5 is happening, you can start adding hours - add 1-2 hours to your daily photoperiod once every 1-2 weeks. Once you get to 22 hours/day, hold there for a while and monitor things
7) once you start to see nutrients really dropping, you may consider backing off on the photoperiod...you don't want to overshoot and bottom out the nutrients and cause the growth to reverse. I wouldn't expect that to happen, but you also don't want to intentionally cause that

I think the root of your issue is likely cleaning too frequently, and maybe too aggressively. But - let me know if you think I've accurately described your process of cleaning, I've made some assumptions here - correct me if I assumed wrong, this might change my advice!

 

Correct - you might try this for a while and see if you can kick-start the nutrient reduction: instead of scraping with a chiseling action - with the blade angled into the direction of travel - use a "dragging" action. This will sort of tear the growth away instead of actually scraping, and it tends to remove the outer layer while leaving more small stands attached to the screen.

Also you can use the corner of the scraper to clear the growth off the screen more aggressively, but make an "X" pattern on one side (scrape lines about 1-2" apart) and then on the other side make a "#" pattern or tic-tac-toe pattern. So this way, you are removing growth completely, but only on one side. Then you will have parts of the screen that have growth removed on both sides (where the patterns intersect), growth on just one side, and spots with growth on both sides. This allows both light to get to the base (from both sides) and lets water get there too.

These techniques generally result in no gap in filtration - the reason you might have elevated nitrates could be because when you clean too aggressively, you have little to no filtration, so the scrubber isn't ever getting caught up after this gap, and when it starts to, you clean it again.

This should break the cycle. I would try these techniques first and leave the lighting where it's currently at (16-18 hrs/day, no diffuser)

 

Absolutely!

 

Growth could be related to the lights (spectrum, intensity, etc). Are they a pretty close match to what you had?

 

Slow growth right in front of the chip sounds like a bit of photosaturation - intensity is high. The single-chip theoretically should have been worse in this respect, 30W peaking in one spot versus 5 W peaking in 6 spots. I would expect that growth would fill in, but you might consider backing off the lights slightly (like 1/2", not much) and seeing if that helps.

The other thing you could do to cut the peak intensity right in front of the chip is diffuse the light right in front of it. I would suggest attaching that to the scrubber body, not the light (heat is the issue). If you have some diffuser material, like from a 2x4 or 2x2 grid ceiling light fixture, you can cut a small piece (maybe 1" square, possibly less) and some double-stick scotch tape and place it there, might only need it temporarily.

Another option is to split up the photoperiod until the screen fills in.

Usually this effect is temporary

 

Looks like 10 chips each, and they have lenses also? The lenses are meant to throw light far and keep it focused. Generally what you would use for hanging these over plants, most fixtures are made that way, but for a scrubber you want that light to spread & blend. Not sure if you are able to remove the lenses, but I would look into that. Some fixtures are rigged to shut off when the lenses are removed. Also if those are rated (IP6x) then that would obviously make the unrated...diffusing might be your only option (that and backing them off)

 

I never said those lights are unsuitable. I don't have enough information to make that call...just throwing out ideas of what you can do to make them work.

It would help if you had pics of how the screen is growing under these lights.

Take a pic of the lights with them turned on

Also do you have a link? Might be more info on there.