I would doubt this was algae. An algae bloom is green. Whitish normally means bacterial bloom, and this is caused by high organics in the presence of light.
The plant fertilizer being dosed was LeafZone, and this only contains two nutrients, iron and potassium. The other 15 plant nutrients would have to occur from elsewhere, and likely won't be sufficient to balance. You don't say how CO2 was "dosed," but here again, if the other necessary nutrients are not available, adding CO2 will not benefit.
Fish foods add nutrients obviously, and water changes will help keep them in balance. Be aware that daylight during summer is longer and brighter, and this can be an issue depending upon the balance between light and nutrients, plant load and fish load.
The first nutrient supplement to add to a planted tank is a comprehensive liquid, as this will supply all nutrients in correct proportion. As the balance increases (more plants, higher light, added CO2) the supplementation has to increase to balance, and you might move to a different regime such as dry ferts. But from what you've told us here, you are still at the lower level of balance so something like Flourish Comprehensive Supplement (probably 1/4 teaspoon once a week) is your best additive. Brightwell Aquatics' FlorinMulti is another that works the same.
Byron.