The standard answer for pinholes seems to be lack of K, but this is a high tech EI tank dosed with:
KNO3 - 1/4 tsp (2 dashes) 3x weekly
KH2PO4 - 1/16 tsp (1 pinch) 3x weekly
K2SO4 - 1/16 tsp (1 pinch) 3x weekly
CSM+B - 1/16 tsp (1 pinch) 3x weekly
CO2 - light green, on 1 hr before lights on, off 1 hr before lights out.
I do not use GH Booster; local tap is 8.3 dGH. Dosing is appropriate for 20-40g tanks; this is in a 29g.
Light is high 6 hours, medium (or less) 2 hours. Floater cover was removed a week ago and pinholes developed. Also see some in Ludwigia while new hygro is losing leaves and vals have detached at the substrate level.
Root tabs are used, though I'm not exactly sure when next-to-last application was. Last application was a week ago, but they were old tabs and erupted to the surface.
Substrate is eco-complete, so it should be fully charged from a year of EI dosing and root tab leaching.
ETA: tank has four tetras and a dwarf gourami who are fed reasonably well, plus there are two snails who clean up leftovers, so the fertilizers above are further supplemented.
Am having a BBA outbreak so I'm cutting the photoperiod to 4x high plus 2x medium.
I hate the thought of adding more KNO3 - I already can't keep even ghost shrimp in this tank. Adding more nitrates may make it impossible even if I figure out my mistakes with shrimp.