chlorine types & low readings, pH vs. Alkalinity, motor operating cost, backwashing

I have inherited the task of pool maintenance, so I have some questions on the fundamentals.
With respect to maintaining the chlorine level of the water for a correct reading on the test strip what is the difference between the liquid chlorine you buy in the yellow refillable liquid chlorine containers, and oxy shock (the pale I have now states "chlorine free" on the label, and the "stabilized chlorine pucks/owder" that gets used everyday? Lately I use a floating thingy with a large chlorine puck, permanently releasing a small amount of chlorine. I believe this is the same type of chlorine as the powered stuff, which we used to do, but we use the pucks now for convenience? (or is it!?). I am getting a low chlorine level reading every couple weeks when I do the water test (strip). Should I be using more pucks in the floating thingy at the same time in the container (like 3, 4, or even more in the container)? I currently generally use only 1 or 1&1/2. I also have pH up, pH down, etc. chemicals for when the water test tells me too, and algecide chemicals for instance for the obvious. clarifyer, stain remover, stabilizer, condition: in no combination or order. I only need to know about chlorine, for the low on the strip problem: what chlorine I should use and when. Should I have slightly low readings every couple weeks, is that common, or should I fix this; should everyday use be enough Cl. And how often is a common need for the yellow refillable liquid chlorine containers, or otherwise oxy shock. I don't know why "chlorine-free oxy". I currently use the oxy shock infrequently when I'm told to, but I use 2/3 of a yellow refillable liquid chlorine container every two weeks or so when the strip reading is quite or slightly low.
In chemistry class I learned a little about "pH", isn't alkalinity and acidity (pH) just the opposite ends of the same scale. So why are pH & ppm Total Alkalinity two different variables on the water test strips I use? ppm Total Bromine and ppm Free Chlorine are the only other two test variables on the strip. I notice Total Alkalinity is preceeded by ppm, as are all the other factors except pH.
I have a pool pump and filter, but no heater. How do I determine how much electricity the pump motor is drawing? When the pool was installed they put in a seperate circuit breaker under my fuse box. I think this motor is between 1/2 & 2/3 hp, so say .6hp. I painted it, and there is no sticker on it anymore. Assuming I can properly identify it (how do I do that), How do I calculate how much it costs to run (operate) it using W=V*A, then my kW/h cost from the hydro bill. I don't even know if its 110V or 220V.
Iirc, my filter is a jacuzzi FM pool filter, originally beige. I guess its called a sand filled type. Nothing special, by eye its about 27"H x 19"Round. The motor/pump was purchased seperately from the filter. The only positions the lever handle goes into ever is filter or backwash.. I know little or nothing about ho it works inside. I was told to do a short backwash after a lot of filtering or vacuuming to clean out the sand, releasing the trapped particles of dirt, etc? Is this correct, should I always backwash after vacuuming? What happens inside,; does the water reverse direction or something; travel top to bottom, or bottom to top? What is the point of the other settings: winterize, rinse, test, drain, and whirlpool? We had our vinyl lining replaced and they eliminated the plastic drain cover with flat continous vinyl at the lowest point in the deep end after cementing, and disabled/removed whatever else, saying it was a useless feature after all.
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