I noticed this gap earlier. Backstory was that the deck was poured, demolished, and then poured anew at the end of construction. The white stuff is perhaps efflorescence. Ground was waterlogged for a time and the white stuff disappeared entirely, now the ground is drying out and white stuff returned.
The cracks seem like maybe cause for concern. TFP must know what this is all about and what it means. If I missed a link in my search, apols.
Pool chemistry is balanced per TFP methodology with no 'innovations'.