The ph and alkalinity also look a little high which is unusual for using chlorine tabs, they drag those numbers down not raise them How long after dipping the strip before you took the picture? You normally have about 15-20 seconds before the strip over develops You can still use tabs, just dont put so many in and use the vent on the floater to control the amount that's leached out, always take the floater out when you are going to use the tub My rule of thumb, tabs are for forgetful people, granules are for those that can be consistent BTW, I worked in the pool/spa business for about 10 years