Ok so I did my regular backwash of my lava rock that I do every couple months. I've done this a few times no issues. Tested my water and all parameters are great. (Nitrates, nitrites, ammonia, ph, etc.) My ph is high but I don't think that's the problem as it has been high for a while now without issue. Noticed three fish in my skimmer basket this evening that looked dead but when I picked them up they were still breathing and moving so I put them back into the pond. The began floating on their sides then erratically swimming in a disoriented and strange manner and curling their bodies. I took them out and put them in a bucket. Came back in ten mins and found 4 more fish exhibiting the same behavior. Removed them as well. Every ten mins or so another one or two would start doing this as well. I'm now up to 15 goldfish that seem to be sick or who knows what. All have been removed and are in a bucket. 4 have died. One of the ones that died looked bloated and a little beat up but the others don't seem to be "bloated" per say. The only thing I can come up with is maybe poisoning? My husband spread some tick/ pest killer granules in the yard today but he said he was very careful to not get it into the pond. My koi, minnows, shubunkin, and other the other goldfish seem to be under no stress at all and are acting completely normal. I tried attaching a video but it won't let me so attached a pic instead. Some are at the bottom, some at top, some on their sides or even upside down before going nuts swimming frantically shaking, gulping, and curling. Any help or insight would be greatly appreciated! I'm scared to death I'm going to wake up to a pond full of dead fish in the morning!