What's the best way to replace the Purigen and Chemipure Elite?

I use both Purigen and Chemipure Elite in my aquarium as part of the 'chemical filtration'. It's been nearly 6 months and I think it's time to change them out. Do I put the new bags in with the old ones for a little while, or will the bioballs and live rock supply enough bio-filtration that I can just take out the old ones immediately?  

My phosphate level was .25 which I think might be another indicator that it's time to change the Purigen. Would you agree with this assumption?

I know I can regenerate the purigen, but I just don't want to take the chance using bleach and accidentally killing everything in my tank. Besides.....I have a 1/2 a bottle of left over Purigen from the last time, so all I'll need to to is get two fine mesh filtration bags to put it in :) 

If you have any advice, I would greatly appreciate it! Thanks 

Thanks TommieLynn! I had a 1/2 bottle of Purigen left over from the first bag I filled so I just took out the old one today and poured the rest of the bottle in the new bag. Next time I purchase Purigen I plan on buying the type that's already pre-bagged. The bottle I had said that the contents would treat up to 250 gallons of water (I only have a 29 gallon tank), so I'm sure I used more than I needed to (I'm confident that won't hurt anything, its just a waste of money). I'll wait a week as you suggested before switching out the old bag Chemi-Pure Elite for a new one. The LFS I was at today only carried Chemi-Pure (not the 'Elite' variety), the employee told me that there wasn't a significant difference except for in price. Is this true? I didn't purchase it, because I wanted to wait and see what everyone else thinks.