Also, I should mention "Chas' Law" at this point: all new tub owners should drain/refill their tubs at the end of the first month of ownership. This is for your health, safety and mental well-being. Most new tubbers over attend their babies during this first month. They also give up more skin oil and other contaminants as well as just flat out USE the thing more than they will down the road.
So the intial fill water gets hammered early. Change it at around 30 days. It's not real important to get 101% of the water out, just turn off the power, drain and refill. Keep the lid on so any residual heat can be retained to help it reheat faster. You'll be glad you did.
Enjoy.
8-)
No dump for me yet.
It's been 11 weeks since my initial fill and besides a relatively high CYA my water is perfect. I've only added ph or alk + or - chems twice. 8-)