Algae Help

So I have been collecting rain in a white plastic barrell. I noticed a algae buildup inside the barrel turning the water a green tint. I plan to scrub the barrell out with bleach water then paint it black. TO help keep the light out of the water.

My question if my scrub/paint job doesnt help is feeding collected rain water that has some algae growing in the water bad for my plants. If I do feed them this water is there anything I should watch for?

Any Help out there?

Personally, I would not feed my plants that water. I would think the algae would eat up some of your soils nutes or mess with the plants roots. Are you an outdoor grower? Maybe you could dis-infect your barrel by scrubbing it down good with vinegar water and bring it out of the light. Collect your rain water in 5 gallon black buckets instead and empty those into your white barrel..