Chemical help needed

[SarahLSam]

Hi, I'm new here and to owning a pool.
Set up our 12ft Bestway Fast Set pool last Bank Holiday Monday. Tested water and followed the instructions received for balancing total alkalinity and ph. Got these to ideal range and shocked with granular chlorine as instructed by Bestway.
Chemicals all fine for the first week. Family visited (1st day of group visits as per Covid guidance) the next week and used pool for one day, 1 adult and 1child for a good couple of hours.
Since then I haven't been able to balance the ph again (too low at 6.8 or less).
Forced in to partial drain as top ring punctured and suffered a large water loss, topped back up with fresh water. Got the total alkalinity and ph back to ideal by Wednesday and steady overnight, shocked again yesterday, but within the hour the free chlorine had dropped to approx 5. Left overnight to wait and see.
I've tested again this morning and TA is between 80-120, but ph has dropped back to 6.8 ish and free chlorine reading 0. Nobody has used pool since Monday and filter has been running constantly.
Can anyone please offer any help/advice on this.
Thanks in advance.
Sarah

[Denniswiseman]

Hi Sarah and welcome
What we need are correct numbers especialy CYA. You really need to get yourself a decent FAS/DPD test kit, dip strips aren't good enough
FC:
TC:
pH:
TA:
CH:
CYA:
Calcium hardness isn't an issue with vinyl pools
Hot sun burns off chlorine quickly, especialy if you don't have sufficient CYA
You need about 40-50 CYA
Excessive CYA renders your chlorine ineffective and you have to use more to get the same sanitation
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach)
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA

[SarahLSam]

Hi, thanks for your response. I'm afraid those kits are out of my price range. I was advised that strips were sufficient, indeed Bestway recommend them. Is there another way to measure CYA and what is used to lower it if it is excessive?
Much appreciated

[Denniswiseman]

Hi, thanks for your response. I'm afraid those kits are out of my price range. I was advised that strips were sufficient, indeed Bestway recommend them. Is there another way to measure CYA and what is used to lower it if it is excessive?
Much appreciated

Strips are commonly called guess strips. Pool stores will test water albiet not as accurate as your own
To lower CYA you need a partial drain and refill but you need to know your CYA to do this. Example if your CYA is 100 you need to remove half and refill. You will then have 50
If you have just recently filled your CYA shoudn't be that high
Bestway are in the business of selling pools and if they say you need a decent test kit then you may not want to buy "Just use these strips which we give you and recommend, it's easy"

[SarahLSam]

Hi, thanks for your help. I'll have to try and get a kit. Much appreciated.