So I was told by one person who is trying to drive some pumps
(the MFG made them hard to do so you spend a mint on the controller)
that you need sine or square wave ac (12 volts) to drive them.
I was under the illusion you could just use PWM to control them but I was wrong.
Can I somehow use the arduino to create variable(control it) frequency AC sine or square wave power?
Sure, no problem at all if it'll really accept a square wave.
Just wire up a standard comparator circuit (lots of examples available through google), and use a bipolar power supply, instead of a single supply (like most Arduino projects do).
If it doesn't need much current, you can use a common low-cost chip like the LM358.
If it needs up to a couple of Amps to drive the motor directly, the L165 is available for only a buck from BG Micro (one of my favorite places to find surplus parts for projects).
Ran
Tanks for the info.
Currenty nobody knows what they run from,
although an engineer who keeps a reef is helping me out.
With all the opinions of what to do I'm trying to get all my options