Have you tested a sample of your tap water after letting it sit out?
Have you tried running the API pH tests again to see if the odd results happened again? I've never had them give such conflicting readings and I've had systems that ran right at about 7.6 for ages so I often ran both tests.
extra rinsing of the test tubes with sample water (three times) before running the tests again might help if perhaps you used one of them to test something else that might have had a drastically different pH.
I retested my water in both my aquaponics system and from the filter. Aquaponics is still at least 8.8 and filtered water is right at 7.0. Any suggestions for pH down? I was going to use earth juice pH down on the advice of one of my friends and fellow aquaponic grower.
When you say the filtered water is right at 7.0. What kind of filter? And did you let the filtered water sit out for a period of time before testing the pH?
I agree that the Hydrochloric acid (Muriatic Acid) is a good choice for initial system pH adjustment. The left over chloride is actually a good thing for a new system that might experience a nitrite spike when you get fish since the chloride ion can help protect fish a little bit from the nitrite toxicity.
Another option for pH adjustment might be to use phosphoric acid. This might be a good choice if one is going to be fishless cycling using pure ammonia and seaweed extract to get the system started up since the pure ammonia and seaweed extract don't provide phosphorus. There are some hydroponic pH down products that are phosphoric acid.