You could easily power 2-3 diffusers with the 3.5 cfm that your pump produces at open flow.I would not suggest using 3 in your situation. Consider 2 units spaced apart with a regulator to slow the system to perhaps 2 cfm and still use a conservative startup.Having one central unit either on or off (all or none) is also risky.Regardless it will take "time" to slowly get your water where it is a higher quality for healthy fish but it will happen.
