yes I am going to use DC to Puls Width Modulator to do it
What modulator do you use? I have pumps for that signal (independent from aquaristic), where I need such a device.

so the relay 1 & 10v 1 both work at the same time - if 0v is set on the software both relay 1 & 10v 1 will be off & if 1V is set both are on?
Yes, that´s right. Same for channel #2