Is substrate an absolute requirement?

[qsaark]

Could be the demand for nutrients has increased. Raise your dosing a little to see what happens. Seems like something is limiting to me.

Dosing of what? fertilizer? CO2? light?

[StanChung]

Ferts and CO2, As total plant mass increases and their root structures expand, they would be hungry for nutrients. To me pearling is indication of photosynthesis. If you had it before and don't have now to me it says something is low. Bear in mind every component in NPK + the micros has to be present for good growth or else the plant will finish up it's stores and start cannibalizing itself.