Nematodes will eat the larvae that will eat your roots--big problem. Unless really bad infestation, the flyers are just a nuisance. These are real easy to use:
Amazon product
On my DIY sips, I use these for drain
DRAIN I put at opposite end of fill tube. When you water the rez, once water starts draining, keep pouring for about 9 seconds. This will help push out any old stuff keeping your water fresh. On the EB jr I tried, put gorilla tape over the built in drain and installed a hose barb. I run 1/2" tubing to jars
On your DIY's I wouldn't have the rez any more than 2 gallons. With 2 plants in each, should last you a week. I started with a bigger rez and had issues with water becoming rancid.