Originally Posted by Knetter
OK! i really appreciate your help guys!...I've ever heard too that the mh lamps degrade when they are getting older. Is it really that the spectral shift does affect plant growth? I think because the lamps are getting less brighter, the plants and thus the algea can "relax" al little bit.
Put it this way: You haven't always had a problem with algae, right? Your dosing regime and CO2 input was perfectly balanced for the lighting you had. Now that the bulbs have aged, lost intensity, and shifted their spectral output, the balance you struck earlier is no longer. You need to adjust accordingly, but the easier alternative to changing your CO2 input and fertilization schedule is to replace the lights and (hopefully) restore the balance you once had.