After being in the 50s/60s for a couple of months, they should be "ready to go" in terms of breeding. Boosting them all the way up to 70-73, however, may make their breeding season fairly short. They lay like crazy in the upper 60s, but when it hits the mid-70s, they think it's summer and quit. Try to keep them on the lower end of that range (even if it means turning off the power filter, if you have one). Let us know how it goes!