I have a 30 long with a coral life freshwater light. It has the stock bulbs. My tank is low tech. The chart in the sticky by Hoppy indicates that I have about 35 PAR now. I would like to start using peat to lower the pH, but not remove the tannins (the tank is a SA Apisto and I would like the "black water" effect). Any idea of the reduction in PAR? I have no way of knowing what the concentration will be, so this may be an impossible question.