I worried about that too, but decided it wasnt that big a deal for a couple of reasons.
The inverse square law is on our side. In all those cheaper - plastic - sterilizers that have a housing surrounding the bulb, the bulb is very close - often touching any plastic parts. However, with just the bulb by itself, it will be easy to suspend it in the tank so its much further from any plastic. I should be able to more than quadruple the distance to any plastic, so 1/16th the exposure or less.
If it did prove to be a problem in my case, a new tote is usually $10 or less on sale. I think I will be able to feel and degradation long before the tote fails.
If the plastic does start to wear, the solution would be easy - just stick the light in a short piece of stainless pipe and direct the pump outflow to force water through it. A short piece of 2" SS pipe should not be too $$ at a metal recycling yard.
Im pretty sure you can also get UV stable plastic pipe. ABS should work fine as its used outdoors as vent pipe exposed on roofs. Im also thinking I read that some forms of plastic electrical conduit - the grey stuff - are UV resistant, but need to check on that. It might be cheaper to buy 16" of scrap SS than a 10' length of pipe from HomeDepot though - and more certain of safe use.
As far as flow rates needed to kill stuff, in a hi flow system - like those zip farms - you will need lots of power or use more UV units. The UV doesnt have time to kill stuff if the water flows through too fast, but if you slow it down, it works fine. The other thing is re-circulating inside the rez will run the same water by the bulb repeatedly to give more cumulative kill power.
I think in our situation a smaller, lower power UV unit would work fine as long as the water can circulate through enough.
I noticed he mentioned needing to add extra iron to make up for the precipitation due to UV. Guess I better look up what specific product I might need to get to supplement any iron losses.
I also need to go back and see which specific chelates of iron worked well and which precipitated the most - then see whats in these AN nutes, Mega Crop, etc. I might be fine or I might need to add something.
Im jazzed about the potential for this, in combination with RO, to stop the algae.
Almost forgot about the bennies you mentioned - if this UV kills the algae without needing any chlorine, or copper, then it will enable the use of bennies if you spray them directly on the roots. You still wont be able to put them in the rez, but thats not a concern for me. In fact, I dont want them in the rez. Even the good bacteria are slimy