Hi Butch - The algae growth is mostly on the tray as a film and peels of clogging the uptake, and allowing bubbles in the edge, thus breaking the siphon earlier than I'd like. I'm going to try a modification to hold the tube down better. The lower, feed line is bent itself up as from the pressure of the flow as it enters the tray. Something I suspected might occur, but it means I can't rely on the feed line to drain the tray fully. I'm suspecting with your smaller tubes, you are using a lower pressure pump? How do you hold your tubes in place?
Hi Gill - Solid question! Can't speak for Butch, but for me the drain line being higher ensures that I can reach and maintain a particular depth for a few minutes to get a good soak. The pump is adjustable, so I have it set to a flow rate that roughly balances the drain line siphon (a little less just for safety). If I had the feed line higher, the siphon would start earlier and either I would be forced to maintain a higher flow rate to get the depth I want, which could result in overflow if the pump didn't kick off properly, or I would hold the water quite low on the pots, and face the prospect of not soaking the media enough. The feed line is lower just in case the pump kicks off too soon, allowing it to act as a back up siphon draining much (though right now not all) of the water. I wasn't worried about head pressure. The increased cost of the more powerful water pump was negligible, especially given the decrease in potential catastrophic possible failures. Does that help? If not, let me know and I'll give it a second go (sometimes the details in my head don't make it to the page).
Hi Yuusui - If you are going to go for a build, let me know. I can tell you where you can get all your supplies locally, and you can borrow my drill bit to make the holes for the tubing. Despite my need to tweak my build, it's really a brilliant system!