LONG REVIEW, BUT PLEASE READ!!! Okay, so my pond is in 100% full sun so I have been dealing with warm, pea soup chlorella (planktonic) algae bloom all summer long. Not bad for the koi, but unsightly to the eye. All I wanted was to see the bottom of the pond and my koi through crystal clear water. Isn't that what all of us koi pond owners want? Well, I finally caved and decided (per my brothers recommendation) to start looking into a non-copper algaecide. I am very familiar with APi products and trust the company, but after doing research and reading up on plenty of positive and negative reviews I was a bit leery in adding an unpredictable and unnecessary chemical to my pond, but I was so tired of the not seeing the true beauty of my koi and the green water didn't smell great either. Please note that all water parameters are spot on: Ammonia 0, Nitrite 0, Nitrate 0, PH 8.2 (evening), KH 14 Drops. Pond is approximately 5000 gallons with a lot of filtration (won't bore you with those details), including a UV filter, as well. Anyway, I called the company and left a voicemail for them to call me back because I had some questions regarding the negative reviews. They did return my call, but I missed it and I never called them back. I decided to purchase the product and dose carefully. A few things I know is that aeration plays an important part when using any algaecide. IT IS THE MOST IMPORTANT THING.....BUT.....Here is my experience with using this algaecide. So, my first treatment went very good, fish acted very normal and they didn't seem to notice anything different. I (Please note; I added each treatment along with a natural cleaning bacteria to help break down decaying algae) By day two I noticed a slight clarity in the water. It was definitely working. I did a 10% water change at the end of day two. I waited the recommended three days before doing a second treatment. My second dose went just as well. No issues and koi were just fine. By the end of my second treatment, I could see three feet down! That's 6 days after the first treatment and water was much more clear. It was working! Now, on day 6 before my third treatment I did a 20% water change to help remove the dead chlorella in the water column and did that using my go-to dechlorinator Sodium Thiosulfate. My intention was to add my third and final dose the next day but I forgot and I added the algaecide right after the water change. As soon as I added it I knew it was a BIG MISTAKE not to have waited at least 24 hours after the water change! DO NOT MIX THIS PRODUCT WITH ANY OTHER CHEMICALS WITHIN AT LEAST 24 HOURS OF USING THIS PRODUCT! All of my koi almost instantly disappeared to the bottom of the pond and some were seen darting around. I though I just killed my beloved koi and there wasn't much I could do about it. Doing another water change with the necessary dechlor would probably do more harm than good so I added 10 lbs of charcoal to the waterfall. I didn't see my koi at all the rest of the day. I thought for sure I would wake up to 27 dead koi in the morning. However, I woke in the morning to find all my koi swimming happily around looking for their breakfast. So my suggestions: AERATE AERATE AERATE (simple waterfall isn't enough aeration) and DO NOT use with ANY other chemicals, especially dechlorinators such as Sodium Thiosulfate. I HIGHLY recommend NOT doing water changes within AT LEAST 24 hours of using this product. That is what will be detrimental to your koi and other fish. If fish show signs of stress, increase aeration and add carbon to remove the chemical agaecide. So, in conclusion, here are the pros and cons of this product: PROS: ~Is highly effective against chlorella algae blooms (pea soup syndrome, I call it) Knocks back Chlorella blooms withing a day or two ~Works fast ~Easy to dose ~Cost effective CONS: ~Will harm your fish if used within 24 hours of doing a water change with dechlor (should say on the bottle, but doesn't). API should put that on the bottle. ALWAYS AERATE. ~Does turn dead carpet/hair algae a very ugly black color after killing it. But that's normal. Hope this helps! Took a LOT longer to see results in killing the little amount of spring algae I had in the pond, but that wasn't my target.