@Reefers , what is the ph of the tap water? Test 24hours after it’s sat out in a bucket or can or glass. It has to sit out a day or it will be off. The gasses in water under pressure take a day to gas off. People get false ph readings from tap water for their fish tanks ALL THE TIME. It’s the same with our plants. Test 12-24 hours at rest or 2-4 hours with an airstone. Anyway, if you are not starting above 7.0 I would stop adding coffee. My gut reaction was too low ph. But to know for sure you would have to over water a tad and catch the runoff in a clean bucket. Test runoff for ph.
I may be wrong, but didn’t you say you also used a sulphur product for ph down in another thread? Sorry if I am wrong on that, I have read a lot of threads😊. If sulphur product is in your mix + coffee ph downed water you may be getting a tad too low ph. That looks like low ph to me.
And It’s so easy to test for.