As mentioned already, I would recommend heading over to Trouble free Pool. I just bought a house w/ pool 3 months ago and have been learning the ropes on the trouble free method which is essentially manually dosing with liquid chlorine and not using any of the crap they sell at Leslie's. I have now completely moved away from 3" tabs and use liquid chlorine...I haven't had to "shock" the pool or add any chemicals for over 2 months now, I just maintain a proper chlorine level with liquid bleach based on the CYA level of the pool.
Since your pool is green more than likely your chlorine level is way of out whack. MY guess is you have been using chlorine tabs which has put your CYA level over the top and essentially made your chlorine less effective, this is the primary drawback to the 3" chlorine tabs and over time is not sustainable and will lead to issues that require expensive chemicals or starting over due to algae buildup.
My recommendation
- Buy TF-100 test kit. This will allow you to accurately measure chlorine to 0.5 ppm and determine your CYA level. Do you have any test results that you can provide?
- SLAM the pool. This is essentially raising your chlorine to the proper level and MAINTAINING to kill all active algea in the pool. I did this and it was a 4 day process of running the pump 100% and adding bleach every day. Throwing a bunch of shock in the pool is not going to get you there and only going to cause other issues (like raising your CYA or hardness). You are done once your pool is clear, and you drop less than 1.0ppm of chlorine overnight (this indicates there is not a significant amount of microorganisms in the pool to cause algae and consume chlorine). SLAM process at link below:
http://www.troublefreepool.com/content/125-slam-shock-level-and-maintain-shockingl
- Once done you let your chlorine level drift down to target level based on your CYA. Chart at link below provides guidance. You could go back to 3" tabs but I would recommend you seriously consider switching to liquid chlorine as it will give you a "trouble free" pool. You can either manually add the liquid chlorine daily or get an automated feeder or salt system.
http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock
Just for reference....During the SLAM I used about 4 jugs chlorine at $3.99 a jug and performed daily brushing. The pool cleared up quick and has now been perfect for over 2 months. WAAAYY cheaper than the 4-500 you are being quoted.
I would also like to add the Leslies/Texsun will not give you any of this advice and will not mention anything about CYA/chlorine relationship....their business model is all about the pucks and shock which take your CYA sky high and then sell you other more expensive chemicals (e.g. phosphate free!) to battle issues since your chlorine has become less effective.