Take a breath.

Did you check the ppm of the runoff?

Fresh FFOF _will_ give you very low runoff pH. If you've only been in the 5 gallon for a week, chasing pH runoff is going to result in disaster.

I nearly freaked the first time I checked, it was also in the area of 5 out (in @ 7). Seemed impossible, so I did a soil test. Soil tests pegged it at 6.5. The FFOF is buffered pretty well, adding a little additional lime should have helped to stabilize it even more.

I honestly doubt there is a real soil pH problem, other than variation of the water going in. Keep it ~6.8 with the FFOF.

Don't panic too much if they start looking worse, before looking better. Slugging them hard with that 8.0 stuff may piss 'em off.