powerhead in a green water bottle.

I think a power head is overkill.

All of the GW setup's that I have ever seen just use air bubbles and are successful.

I guess you could try. But the most expensive air pumps I have seen are only $12 so it is a very minimal expense.

Are you only setting up one culture bottle?
I plan on running up to eight containers off of my $12 pump and I don't see a way to run multiple cultures from the power head.

It would be useful in mixing the saltwater for the cultures though.

The benefit is that if you have a crash in one culture you don't have to wait ~10 days for the new starter to ripen. Most cultures are contaminated in some way and will crash eventually. Also, depending on how often you are planning on adding the phyto and for what purpose, 5g may not be a large enough culture for 65g.  

I grow in 10 gallon tanks and run a Rio 800 that is near the bottom to make sure anything that falls out of suspension is whipped back up.

I also run a airpump/stone in the tank.

i keep piece of acrylic on the top of the tank to help prevent contamination.

-dwn

thanks for the offer Mark. I might take you up on it if what I have doesn't
work. I have one pump that does 2000cc 4.0 P.S.I. Whatever that means. I
don't know if I could aerate two bottles with that or not. I alos have my small
powerhead so I'll try both things and see which one works better. As for
bleaching the powerhead, how long do you think i should bleach it? It hasn't
been in my main tank for quite some time but you never know if there's
been contamination somewhere.