Cannot keep chlorine in pool

[maf528]

I've run out of ideas on my own, so I turn to this forum for some help. Since I opened my pool this spring I have not been able to keep any chorline levels in the pool for even 24 hours. In past seasons, I could keep 3-4 pucks in the floater with some occasional shock and levels would maintain all summer. However this year, I can fill 2 floaters and shock and the next day be at 0. I've read that different algaes or phosphates could cause high chlorine demand, so earlier this week I treated for both (even though the water had been clear all month). Then last night I backwashed and added 9lb of shock around 7pm. Now at 8am I have maybe 1ppm left. My other readings are:
Hardness ~250-300
Total Chl 1ppm
Free Chl <1ppm
PH 7.2
Alkalinity ~130
CYA was 49 when I had it tested at the store, but the dipstick today looks maybe a little lower
Pool is approx 25000 gallons, gunite, in-ground.
Thank you!

 

[IceShadow]

There could be a lot of different things going on. The first thing to do is to have a way to test your water yourself with your own reliable test kit. Test strips are notoriously inaccurate and pool store testing is hit-or-miss, and we don’t know if yours is a hit or a miss.

A TF-100 from tftestkits.net or a Taylor K-2006c kit from Amazon (the “c” is important) are the recommended kits that have all the tests needed. Once you have those and post a full set of test results, it should help us to help you with an appropriate course of action.

It will also help us if you can fill out your signature. See mine as an example. If posting on a mobile device, turn sideways to see it.

The most likely answers are either that you have an algae bloom starting that’s eating the chlorine as fast as you’re putting it in, or one of the chemicals the pool store sold is eating it up. Do you have a list of everything added so far?

 

[maf528]

Thanks I do have a smaller Taylor kit, but it doesn't test for CYA. I will look into upgrading.
As for the chemicals, when I opened this spring I only needed to add some PH Up (sodium carbonate) and some Clorox brand Stabilizer (which says 100% CYA). It wasn't until I got desperate this week I went to Walmart and got Clorox Phosphate remove and Algaecide, but the problem was there before adding those 2 anyway. Should I assume an algae bloom even though I don't necessarily see it? If so, what else should I be doing? Thanks again.

Edit: I've also used lots of 3 inch trichlor tabs and shock

 

[IceShadow]

What was the algaecide and the shock used? There might be something in those that could cause chlorine demand.

While waiting for the kit, add 3ppm of FC daily (if your pool is clear). If the pool goes cloudy or green, then add 5ppm daily. Use liquid chlorine for chlorination. Once you get the kit post your results and we can really dive into it. May need a lot of liquid chlorine so find a source for that for sure.