pH of 6.8 is WAY low if it REALLY is 6.8! How are you testing? Taylor k2006, DPD tablets, OTO/phenol red, guess strips, or pool store? If 6.8 is the lowest reading your test reads, getting that result means 6.8 or LOWER (maybe 6.2). pH below 6.8 can damage your pool. Since we don't know how big your pool is, we cant advise on how much it will take to fix this. Go to WalMart and get 2 boxes of 20 Mule Team Borax. If you don't have a Taylor K2006 or a drops based OTO/phenol red test kit, get a DROPS based OTO/phenol red kit.
1. Add 4 cups of the borax SLOWLY through the skimmer, don't "choke" it.
2. Wait 1 hour retest.
3. If pH is still below 7.2, repeat steps 1 and 2.
If you are using Intex a "replaces Intex" cartridges, you NEED to get the good cartridges referenced here
http://pool9.net/intex-ssr/
You should get familiar with ALL the information in the first post. It will make maintaining your pool MUCH easier.
Good luck!
Pappy
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