As for the Borates not helping, this link gives some info on borates inhibiting algae growth. The algae listed are Scenedesmus quadricauda, Scenedesmus subspicatus, and Microcystis aeruginosa, where the first two are green algae and the last one is a type of black algae. Though there are many types of algae, the three main groups we describe for pools are 1) green algae which are plants in the phylum Chlorophyta which contain chlorophyll a and b, 2) yellow/mustard algae which are in the kingdom Chromista (e.g. phylum Heterokontaphyta class Xanthophyceae with a cell wall of cellulose impregnated with silica) which contain chlorophyll a and c, and 3) black algae which are in the phylum Cyanobacteria (sometimes called blue-green algae but they are not plants) which contain chlorophyll d and/or f. 50 ppm Borates has roughly 50% or more inhibition against green algae, a small uncertain amount of inhibition against black algae, and an unknown inhibition against yellow/mustard algae. Given how yellow/mustard algae is generally more resistant to chemical attack in general, it is not surprising that the borates are not very effective against it.