# Dropping from 40 PAR to 20?



## Doc7 (Feb 27, 2017)

Hello all,

As per this thread from 18 months ago https://www.aquaticplantcentral.com/forumapc/lighting/132938-lighting-40b-two-stingrays.html i am running 2 Stingrays on a 40B tank. Using 1 layer of window screen I am running 40 PAR on bare substrate at the bottom. I am moderately planted with floating plants on 15% of tank surface (can't really get more due to surface flow characteristics, nor do I want more as I don't like floating plants much anyway)

I am thinking of adding a second layer of window screen to drop my PAR to 20 at the bare substrate level. I am sick of algae on the glass and stringy green algae on my plants which I have been dealing with for many months now. I dose 10 ML of Metricide and dose almost a full EI Regimen, both of which exceeds typical "low tech tank" regimens, and still haven't knocked out the algae. Only thing I can think to do is reduce light. What do you think?


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## hoppycalif (Apr 7, 2005)

Do you use any CO2? DIY CO2 works fine on tanks with less than medium light, and it works even better if you also use Metricide/Excel. I am using a pair of 2L bottles generating DIY CO2, with yeast/sugar. I have only 1/4 tsp of yeast and one cup of sugar per bottle. They last more than 3 weeks each between re-starting them, at staggered times. My light is around 30-40 PAR.


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## tiger15 (Apr 9, 2017)

40 PAR in a bare substrate tank is medium light, and with plant shading, it will cut PAR even further to low light regime. I don’t see any benefit of cutting PAR by half with window screen as there is barely any light left for growing any plants.

I think your algae issue has nothing to do with light intensity, but something else out of balance. Perhaps dosing full EI is too much for a low tech medium light set up. How are your floaters doing. If they look sick, something is out of balance in your water column as floaters can get plenty of CO2 from air.


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