led scrubber fine tuning issues ! advice please

ive recently added a second light to make it a 2 sided scrubber but having a few issues so looking for some advice ,the problem is the centre of the screen appears to be balding/burning ,I presume this is due to to much light but im a little confused as to why this would be
here are the specs
4.5" by 4" screen
good flow at recommended level from return pipe
2 lights featuring 4 osram 660nm leds in a rectangle and driven at 700ma ( there were 5 on each but I removed the centre one as I thought that could be causing light saturation in the centre )
one light on outside of tank other suspended inside
feeding approx. 1 cube daily
diffusers used which are approx. 10mm off front of heatsink
lights are approx. 90mm from screen ( this is from actual leds to screen ) they were closer but ive moved them back to try and reduce the bald area
lights on for 10 hours - 2 split 5 hour periods
so my questions are:
how come the L2 doesn't have this problem when its using more leds and they appear to be much closer to the screen ? how close are they ?
how far from the leds is the diffuser panel on the L2 - as in are my diffuser panels to close to the leds and thus not doing much to spread the light ?
is running the leds at 700ma an issue ?
what distance from the screen are others successfully placing similar lights ?
any advise much appreciated

 

hi turbo
thank you for the info ,its been running as a 1 sided for a few months and I added the second light about 4 - 6 weeks ago and that's when I started getting this issue ,its been a bit better since I moved the lights a bit further back but of course that's caused a lot more light spill ,I think the diffusers would be a lot more effective if they were at 1" rather than the 10mm at the moment as I don't think this is producing a very even light with them so close to the led , is there a way of wiring the leds to half the 700ma to 350ma using the same driver I only ask as I seem to remember some mention of doing this for blue leds to reduce intensity
thanks

 

hi everyone
an update and a few questions
having rearranged the pipework to the scrubber a little I now have the lights an extra couple inches from the screen and this has solved the uneven growth problem ,the scrubber has been running since January and second light added around march , the thing im rather confused with is having worked out my feeding is about 1/2 cube a day when added up over a month is how come im getting thick green algae growth on the screen and algae still growing in display tank ( not massively but still there ) and getting a a daily dusting on glass and and plastic weir cover ,sometimes this is a thin brown film and over times a fine green dusting , I can,t seem to increase my scrubber lighting phase beyond 10 hrs ( 2 x 5 ) with out burning the screen so that doesn't appear to be an option
the tank has always tested zero for nitrate and phosphate ( using hanna checker ) though obviously there are nutrients available for the algae
so im running a way over powerful scrubber for my feeding regime and getting good growth and also a high end tunze skimmer rated 5 times tank volume yet still have nuisance algae after 7 months of adding scrubber ? im aware of the idea of nutrients leaching from live rocks and just interested to hear others experience as to how long it took there scrubber to clear there display tank of nuisance algae ? is my scrubber playing catch up removing nutrients that have built up over time and will one day the display tank algae suddenly start to disappear ?
any feedback much appreciated

 

flow is from display tank return and ive measured it at approx. 900 litres an hour at the screen with screen being about 4.5" wide so at or above recommended level if I understood correctly ?
so do you think the problem is down to the scrubber not working hard enough one way or another ? or is this a familiar situation with the time its taking to clear nuisance algae ?
thanks

 

yes I must say im very dubious about the leaching theory especially after running for such a long period - I don't have any pics of what I get off the screen but Ive just taken a couple pics of the screen ,ive been cleaning sides alternately so first side is approx. 14 days growth second side about 6 , I tried cleaning both at once for a while but it dramatically slowed the screen growth down , I only use RO which has 0 tds and the only supplement I use is kalkwasser so im rather baffled as to the source of the nutrients