At 50ppm B concentration, one should probably consider borates to be a growth inhibitor rather than an algaecide. From most of the data it is shown that it takes far higher concentrations of boron to be significantly biocidal (~ >100ppm).
When I borated my pool water, I noticed an almost instant (24 hours later) increase in FC level with the same SWG %. I was then able to turn down my SWG by approximately 15% absolute output (60% to 45%) to maintain a proper FC. I surmised that the borates helped inhibit the algae growth rates and likely gave the SWG a little more "breathing room" to operate.
That said, borating your water is by no means a replacement for proper water chlorination and I rely on borates more for their pH control than any other aspect of their chemistry.
Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006