You're getting wonderful advice.
The reason the CYA test showed zero is because you don't have any. You're going to need some as mentioned above.
At 28,000 gallons you need to add 7lbs of stabilizer to get you to 30ppm CYA. Since we're not sure if you're fighting an algae bloom on not I don't suggest adding it to the skimmer. You should tie it up in an old sock (or a new one) and hang it in front of a return. You can massage the sock to help it dissolve.
If you have some Cal-Hypo left you can use it to bring your FC up. Add 1 lb of it.
If you don't have any left you need to add 1½ gallons of bleach right now. This will get you through today.
Have you learned how to use the Pool Calc yet?
The reason the CYA test showed zero is because you don't have any. You're going to need some as mentioned above.
At 28,000 gallons you need to add 7lbs of stabilizer to get you to 30ppm CYA. Since we're not sure if you're fighting an algae bloom on not I don't suggest adding it to the skimmer. You should tie it up in an old sock (or a new one) and hang it in front of a return. You can massage the sock to help it dissolve.
If you have some Cal-Hypo left you can use it to bring your FC up. Add 1 lb of it.
If you don't have any left you need to add 1½ gallons of bleach right now. This will get you through today.
Have you learned how to use the Pool Calc yet?