Yes it is 1 gallon. It's a store brand (pathmark). It does not give the % on the label. I've tried to look up the % on the web without any luck. The directions match Clorox so I'm assuming it's 5.5. I've just ordered an ammonia test kit to see it that's my problem. Just a long shot chance. Last year I did have a major issue with one of the algaecide. The product name was United Chemicals Black Treat 3. It was a very weird problem, after adding this product, whenever I added chlorine, it would turn the water light green. By morning it was back to crystal clear. The water tested positive for metal. I bought a magnet/powder from my local pool store and mixed it with the earth. I did this along with few partial refills and the problem went a way. I'm thinking this may be some sort of residual from that problem. Any thoughts on partial doing partial refills. I have not been able to confirm the algae (smear test) due to me scrubbing it away on Saturday. I cannot see an algae present right now. One thing I have not been doing is running the filter 24/7. I reread the article Watermom put up and they suggested running 24.7 I am going to start doing this today.