406303A Black Algaetrine Swimming Pool Algaecide & Deposit Control, 32 fl oz, White

This algaecide worked very well to kill the black algae. Plus it killed the small amount of yellow algae. Only downside is the pool chemistry has been difficult to get back to normal. Chlorine lock problem required shock and PH has been at 7.2 for over a month without adding acid.

One application killed the black Algee in my pool

I have learned since moving into a house with a pool over 25 years ago to get ahead of any algae bloom. If persistent brushing, keeping the chemicals perfect, and 24/7 running the pool doesn't work - this is the ONLY product I have found that will actually get you back to a sparkling pool. Pretty darn pricey though so believe me I try everything before I go to the Black Algaetrine and always have a bottle in the shed. A 38,000 gallon pool usually only takes one bottle - but I don't let it get emerald green in the first place.

This is the only thing I use.. works great

I bought McGrayel Algatec twice, once at the recommended dosage and once at twice the dosage. Black algae came back both times. I tried one bottle of this product and the black algae is gone.

I don't understand all of the good reviews. This didn't work for us at all. We didn't even have black algae, just some of the regular green stuff. Our pool is old and the walls are rough which means we do get some green algae growth in the rough surface which we can't easily brush off. So we followed the directions as given. We checked the water was balanced, it was perfect. We hired scuba tanks and got in there and scrubbed and scrubbed and scrubbed. Cleaned filter, vaccummed. Then we applied the product. Water went very cloudy. Ran the pump. Got in there again the next day - vacuumed, cleaned filter, and scrubbed and scrubbed and scrubbed, but none of the algae was dead or gone. The water was still very cloudy. Cleaned filter again, ran pump. Vaccumed again, cleaned filter again, scrubbed again. Water still very cloudy, no change to the algae. 3 days of hard work.Checked the water and wow, the alkalinity and PH are now off the chart! Took a water sample to the pool store and they advised us not to use the pool, it wasn't safe. We should change the water.So now we still have the algae in the rough surface, have spent 3 days on the pool, and the whole thing has to be drained and refilled. I'm so mad. How others are getting instant results with this stuff I don't know because it didn't work for us at all and cost us hundreds to drain and refill the pool.

Had a bad outbreak of black algae in our above ground pool. Treated twice and it's gone! Best stuff I've used thus far.

After returning home after a long absence, I found that my chlorinator and pump had stopped working and I had a pool full of green and black algae. I started treatment with my usual green/black agaecide which killed the green algae, cleared the water, and got rid of most, but not all of the black algae that had formed on the bottom of the pool. The pool is gunite/pebblecrete which makes it more difficult to remove black algae. After several weeks of brushing and vacuuming, the bottom of the pool was improving but just marginally.I decided to try this algaecide to see if it could totally eliminate what looked like huge stained areas of the pool bottom. This algaecide is a totally different formula than my previous one, and unlike the other one, does not require super-chorination (shocking) of the pool when using. I used half the bottle in my 11.000 gallon pool in each of 2 applications a couple of weeks apart. It seems like it continues to work for 2-3 weeks after application, as every few days for several weeks I noticed the dark areas getting lighter. The key is being patient and brushing with a stainless steel brush every few days. After 2-1/2 months, the dark areas are almost completely gone and the bottom of my pool is back to the Caribbean Blue it's supposed to be.