Interesting; what are you testing to come up with such a low pH? And how are you using the phosphoric acid? Are you using raw or used coffee grounds? Used have a pH in the 6 point something so they're not that acidic.

PH meter for soil and also use it to measure the water. A tiny bit diluted in 1.5 gallon watering is what I use (Home Depot concrete etching). It was requiring too much vinegar to get my 7+ PH tap water lower.

Arrived as two leaf seedlings (regret not getting larger ones). Lowering the PH stopped the spread of leaves dying that was happening at both ends. Sun is in backdrop making these appear N deficient but they are very green. Indirect sun or early/late sun.

Oh ok cool; do you know which meter it is or where you got it from? I'm thinking about getting one myself or some pH strips so I can test for a blueberry I'm growing.

It's a two prong soil moisture/light/PH reader. I only use the PH setting as the other don't really seem to really be useful. I'm pretty sure I got mine at tractor supply.

Lowes has one that is similar:
http://www.lowes.com/pd_251966-83666-1240_0?productId=3028419

Obviously confirm it is calibrated using known PH values (http://chemistry.about.com/od/acidsbases/a/phtable.htm). Some reviews state that a few are bad or go bad.

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Re-potted. Smaller pots and will stick in a corner of green house that has high humidity.

Peat based potting mix, pine fines, perlite, tiny bit of sandy loam, and topped with coffee grinds --> peat and perlite.

Inspected roots. Thick, but very short taproot.