For controlling things, I bought some ebay relay boards "US Ship 4 Channel Way 5V Optocoupler Isolation Relay Arduino PIC AVR DSP ARM MCUBought " from zyltech but they don't see to carry anymore
Just search for 4 Channel 5V Optocoupler Isolation Relay .
Use these relays to control the lower power signals, like the VSP pool pump and spa heater. Also use them for turning on and off sprinklers.
To turn on/off my spa pump motor, needed a high current relay. This replaced the on/off mechanical timer switch it used to have.
Pool equipment manufacturers use something like this
http://www.mouser.com/Search/ProductDetail.aspx?qs=ISjK4nnpKfF4vWP4G80r9w%3d%3d
I used a relay with 110v activation.
But if I had it to do again, would use 24VAC coil, so wouldn't need to use high voltage to control the relay. I have 24VAC available from my sprinkler system. This should work: