Best way to regulate water retention? - SLRPNK

Last year I experimented with a self-watering system for some containers to grow primarily salads and potentially some herbs. They are placed in a way that makes watering a bit cumbersome, and I am typically gone for days at the time during Summer, so that such a setup is very useful to me. It consists of two containers: a top container containing a soil mix and a bottom container filled with water. From the top container, I have a couple of baskets filled with perlite dipping into the water that wick moisture up into the soil mix (I originally used soil for this, which ended up with some nice mold growth :) ). This worked reasonably well, and I had some good harvests of arugula and some regular green salads. But I found the moisture level of the soil becoming too high, especially towards the end of the season when the Sun and temperature were not as aggressively evaporating the water. The soil mixture I used then was a general purpose plant mix mixed with perlite. I was planning on adding even more perlite this year as an attempt to lower the average moisture level, or simply go down to the beach to get some coarse sand and mix that in instead. Any other things I should consider?