Typically chlorine is added to swimmingpools in tablet form, in which the tablet slowly and constantly releases chlorine.
Shock treatments (addition as powder or liquid) can be done as well but requires (bi)daily checking.
To get to 1.5 ppm Chlorine, you need to maintain the level at: 0.3 kg of Halamid into 50,000 liter pool.
To determine the residual Halamid® concentration in water one can do Halamid ion testing in which you measure the chlorine content:
Chlorine can be easily measured using strips, like you can find here.
Or use electronic devices:
See http://www.youtube.com/watch?v=cSlR8VnVkDs for a simple tester from Hanna
Or http://www.testequipmentdepot.com/extech/pdf/cl200.pdf which presents a 1 step process
Multiply the chlorine level by 4. This will give you the residual Halamid® concentration expressed as its initial form (the tri-hydrate compound).
It must be said however Halamid is not very efficient to algae especially once grown, normally quats are used to control algea.