I would think if you are getting 80 to 90 % on pretests you would still study the chapter, but on concepts you have you only do one to three sample problems and concepts that are new you do a more thorough study and more problems. Like you said you don't want gaps in algebra it is foundational.

This is how my son did all of 2nd grade math in one nine weeks. He took each chapter pre test. On the 100% chapters he skipped and less than 100% he only did what he needed to learn and then moved on.

...reading is pleasure, not just something teachers make you do in school.~B. Cleary