The problem is that 13W is too little for 300 gal regardless of the flow rate. The [FONT=arial, Arial, Helvetica]Bunsen-Roscoe [/FONT]time-dose reciprocity law tells us that shorter, more frequent exposures to radiation essentially have the same biological effect as longer, less frequent exposures. It's a well-established fact that UV damage is cumulative. Organisms are not instantly killed by UV but die after the exposure when they are too damaged to perform normal biological processes such as protein synthesis. Those that survive are subject to the energy cost of repairs (to DNA, etc.) that leave it with less energy to reproduce or invade the host and survive its immune response.
However, when you simply don't have enough power, lowering the flow rate is not a remedy because it lowers the turnover rate, leaving the total dosage largely unchanged.
