Black spot algae is the bane of many Kiwi pool owners with stubborn dark specks that just keep coming back no matter how much you scrub! Unlike regular green algae, black spot digs deep into your pool’s surfaces, setting up camp in shady corners, steps, and rough patches. Not only is it tough to spot early, but it’s also incredibly resistant to normal chlorine and basic algaecides, thanks to its protective layers and root system. With the right steps and a few trusty pool care products, you can take back control and restore your pool to sparkling blue for the summer ahead.
Step 1: Test and your water
Keep things easy by starting with a quick test of pH and chlorine before you throw any specialty products at the pool. Aim for pH around 7.2–7.4 and make sure your chlorine is sitting at normal or just above normal levels, so your black spot treatment can actually bite into the algae.
Step 2: Give the black spots a good scrub
Grab a stiff nylon brush for fibreglass/liner pools or a stainless brush for concrete and pebble, then really work over every dark dot you can see. The goal is to break the waxy coating and expose the “roots,” so you get the best outcome.
Step 3: Hit it with chlorine
Right after brushing, boost your chlorine so it is in “shock” territory for the size of your pool, following the directions with EZI Chlor or Granular Chlorine . If you have stubborn patches on steps or ledges, you can carefully sprinkle a small amount of granular chlorine directly over those spots in still water, making sure you follow label safety directions and avoid leaving piles on delicate surfaces for too long.
Step 4: Dose with Backyard algaecide
Once the chlorine hit is done, dose the pool with one of your own black‑spot killers, like Dual Strength Algaecide or Polymeric Algaecide, which are both designed to kill black spot as well as green and mustard algae. Run the pump as per label (usually several hours or more), and keep brushing the same areas over the next few days so the algaecide can get deep into the spots and stop them re‑growing.
Step 5: Clean the filter and lock in prevention
After the spots fade, backwash or clean your filter and vacuum the pool to waste if you can, so you are removing dead algae instead of circulating it. From there, a small regular dose of your chosen algaecide as a weekly or fortnightly “insurance policy,” plus good pH and chlorine control, will make it much harder for black spot to get a foothold in your pool again.
