Nitrates in pool

[waterbear]

nitrates will not directly cause chlorine demand. If you have a nascent algae bloom that might. Exactly what is the ingredient in your granular shock. If it is dichlor return it. for every 10 ppm FC added it will also add 9 ppm of CYA and your CYA is high enough. If it is cal hypo it is ok to use but it will cause your calcium hardness to rise. Let us know the ingredients and concentration and we can tell you how much to add to get to 25 ppm FC.
As far as only using granular chloirne in yoru pool, hogwash! Sodium hypochlorite is what your SWCG produces so you are normally chlorinating with liquid chlorine and if you shock with the unit, also shocking with it! Your pool does not know the difference beween sodium hypochlorite produces in the salt cell or poured into the water from a jug. Also, if you are predissolving your powder shock (which you SHOULD be doing if it is cal hypo0 you are also putting sodium hypochlorite in the water.

Some test strips will bleach out at high FC levels because they use DPD for the reagent (for example, some of the LaMotte test strips). Get yourself a cheap 2 way chlorine/pH tester that uses liquid reagents and has yellow color blocks on the chlorine side of the tester and do the tests I suggested. It is for good reason to help determine the reason you have low chlorine readings. You can pick up such a tester at walmart, home depot, lowes, may ace hardware stores, or most pool stores for a few bucks. If they happen to have a Taylor K-1000 get that one, it's the best one made!

[waterbear]

OK. did a bit of checking. Leslie's Power Powder Plus is 65% cal hypo (they also make a stronger 73% cal hypo, Power Powder Pro). You will need to add 11 lbs all at one time to get the FC up to 25 ppm in a 33k gallon pool. Adding a pound at a time won't do anything at all except replace any chlorine burned off by the sun every day since it only adds about 2 ppm FC in a pool your size and 2 ppm FC per day is normal chlorine loss for most pools.

HOWEVER, as I said before, test with an OTO test kit to make sure that you REALLY have a chlorine demand issue (or possible SWCG malfunction) instead of the test just bleaching out and registering low when the chlorine is actually high. OTO does not bleach out, FAS-DPD can overcome bleachout up to about 50 ppm chlorine levels, Syringaldazine which is used in some test strips, also does not bleach out.
DPD, used in many test strips and most pool store testing liquid reagent test kits does bleach out at FC levels from 3 to 10 ppm, depending on how the strip or test kit is forumulated.

[newsaltwaterpool]

I tested with an OTO test kit and got a low reading of chlorine (0.5), but at least there was a reading.

I haven't added any power powder plus since Monday evening, I turned the SWCG on to 60% yesterday, so that means it is generating something, right? Do you think I should still go ahead and shock with 11lbs of power powder plus?

Forgot to mention, my pH was reading 8.0

[waterbear]

Did you test the water coming directly form the cell? (Turn off the system and loosen a union on the cell to collect the water from the side of the cell going back to the pool when the cell is on and generating.) The chlorine should be very high when tested with OTO--dark yellow to orange to brown color. This will insure that the SWCG is working properly. If not you should try cleaning the cell with acid as per your manufacturer's instructions.

In any case, drop your pH t0 around 7.6, shock the pool, and I believe that you will find that your chlorine will hold after that. You probably have a nascent algae bloom that is consuming the chlorine as fast as it is being produced and shocking will destroy it and allow the SWCG to catch up and maintain the pool (assuming the system is properly working, hence the test suggested above). With a CYA of basically 100 ppm you want to adjust the cell to maintain the FC at NO LOWER THAN 5 ppm. 6 ppm would be a comfortable level to aim for. Also, do not try and test pH until the FC level drops below 10 ppm after shocking. HIgh chlorine levels will cause a false high reading on pH tests.

[newsaltwaterpool]

OK--I shocked the pool last night with 11lbs of Power Powder Plus (65% cal hypo), this morning the pool is cloudy and there is white "dust" on the bottom of the pool. The FC is >8ppm and of course the pH is high at 8. I don't have any other readings at this time but I am concerned about the cloudy water and dust--what should I do, is this normal?

[waterbear]

You did predissolve the shock, didn't you? Also, you did drop the pH first like I said, correct? Most likely you precipitated out some carbonate (and lowered both your TA and CH in the process). This makes me suspect that your TA and CH were higher than you reported (and is a good reason to get a Taylor K-2006 and do you own testing rather than rely on the pool store!) THIS is also the reason I initially suggested using bleach, since it will not cloud a pool . It's not a big deal and it will filter out. Brushing will help. I would suggest getting your water tested (and ordering your own test kit).
Did you ever test the water from the cell to make sure it is working properly?

How are you testing the pH? Some pH tests will read high with FC above 3 ppm, another reason we like the Taylor kits. They are good to about 10 or 15 ppm. If you are SURE that the pH is 8.0 and not just an interference from the FC at 8 ppm or above (how was that measured?) then go ahead and add some acid to get the pH down to about 7.6.

[newsaltwaterpool]

Yes, I predissolved the shock and dropped the ph.

The dust seems to have cleared now but the pool is still cloudy. I just got the Taylor K-2006 test kit and here are my results:
FC - 3 ppm
CC - 0.5 ppm
pH - 7.6
TA - 160
CH - 380
CYA - <30
salt - 3100 (3.1)