Sand filter possibly low on sand ?

Over the past 4 years have never had any problems that were so confusing that we could not easily fix. Have used test strips, and a test at our local pool supply every month or 2 to validate our strips were close.Last month I used the link here and purchased a Taylor K2006C kit to test with and have been using the BBB method since the first week of April of this year taking samples to our local pool store and comparing results with the test kit(very close). We recently went on vacation for a week and came home to a slightly cloudy pool while we were away had 3+ inches of rain and a lot of leaves, bugs , and debris in the pool . Cleaned and shocked to 35PPM and turned crystal clear, now a few days later is very cloudy again. I leave the pump run all the time because I haven't set up a timer for the pool heater/pump yet, and maybe because I figure it won't hurt anything.. My current results of testing are PH=7.4 FC is 4.5 CC=0 Alkalinity =120 CYA=80 Temp =90F, my wife added some chlorine while I was at work today because she said the pool was cloudy, even though it was at 2.5 PPM yesterday. Am I mistaken in thinking that since I have no CC that I could possibly have a sand filter problem? Haven't opened it since we put it in. Any advise would be greatly appreciated. Thanks and try and have a great night. I work 12 hour days and am getting ready for bed, but will check back tomorrow afternoon, I am not ignoring anyone, I just have to get some sleep.

My first guess that is you may have an impending algae bloom as a result of allowing the chlorine to drop down to 2.5ppm. When you have a high CYA reading, you have to keep your chlorine higher than normal. Take a look at the Best Guess Chlorine Chart in my signature below. You will see that with a CYA of 80, you must keep your chlorine between 5-10oom all the time or risk algae starting.

Go ahead and shock your pool. Again, per the Best Guess chart, with CYA of 80, your shock level is 20ppm.

What kind of chlorine have you been using? If you are using trichlor tabs or dichlor powder, you should stop. They are both stabilized which means they have CYA in them and yours is already high. Better to stick with just using bleach.

Tell about your pool. What kind is it, what is the volume, what size of pump and what type and size is your filter?

Repost with more info and someone will better be able to advise you.

Welcome to the Pool Forum!

membership upgraded.

As WaterMom noted, use the Best Guess page.

Question: do the K2006 and pool store CYA results match? (That's very unusual!)

Pool is an Aqua Leader 24' above ground 15,000 gal with a Hayward 1.5 HP pump and 18" sand filter with 1.5" PVC plumbing connections. We were using tabs in a skimmer until about 2 weeks ago, I am not sure if they were stabilized or not. I guess they were because of the CYA level. We figured we would use them up, and our local pool shop said that anything under 120 was just fine when we asked today... Their test results said CYA=95. Thanks for the help.

Added about 3" of water to the pool and then we shocked and let circulate for a half hour, then tested FC. Had to add 3 big dippers to get it to turn pink with the 10 ml sample. I stopped adding drops at 40 it was still a strong pink color. I won't add any more tabs to the pool the supply house says "yes of course they have stabilizer in them". And we are using 10% liquid chlorine from the pool supply . Thanks for the help with everything. Will check back a bit later.

Test your chlorine with OTO (cheap local test kit w/ yellow/red drops) and tell me what color the OTO turns.

What is your K2006 CYA test result? If it's near 100 ppm, DO IT AGAIN, bu this time test pool water mixed 50:50 with tap water.

I don't have a cheap kit on hand, but can pick one up this weekend if needed.
Added 50% tap water to CYA test "3.5ml pool water and 3.5ml tap water" and added 7 ml of the R-0013 reagent and came up with 36 or 37 on the CYA test side.

OK. Just assume 80 ppm CYA, and use the Best Guess chart linked in my signature to set your chlorine levels.

Thank you so very much for the help. Water is perfectly clear, impending algae bloom has been stopped in it's tracks. I may have gone overboard on the liquid chlorine to raise to shock level. My FC is 14.5 and CC is still at 0 pump still running 24/7. How often would you suggest that I check my chlorine levels? I plan on leaving the pool uncovered until the temp gets below 80F . Also what would you suggest that a perfect CYA level be to keep chlorine stabile and lasting the longest amount of time? Why on the Taylor kit is the recommended FC 2.0 to a 4.0 if CYA plays such a roll in levels? Did I miss something?

The Taylor test kit is great. The advice in the book is not. Don't use the book.

As I understand it, and I stress I could be way off base, the Taylor book does not take CYA into account with their recommendations in the book. That would, at least to me, invalidate a lot of what is in that book. A question about that, though. How can a company that makes such an excellent kit not know about something a important as that?

If you want/need to know more, Chem Geek has several posts/threads detailing the relationship, I think.

See the "Chlorine/CYA Relationship" section in the thread Certified Pool Operator (CPO) training -- What is not taught for more detailed info. Even though this chlorine/CYA relationship was definitively determined in 1974 and known before then (in the 60's), virtually no one in the industry talks about it with any specificity. This is primarily due to "the big lie" from the chlorinated cyanurate manufacturers (makers/sellers of Trichlor and Dichlor) that "CYA doesn't matter; only FC matters".