Welcome.
If you are buying natural seawater at your LFS and you live in Murrieta then your water is probably comes from Andy at Oceans In Motion. That's where they are based out of, Murrieta. Their water is the same water that Scripps out of La Jolla uses. It's good water. Your phosphates are way up there, enough so that levels are still that high with all the nuisance algae feeding on the PO4. This is why you are having these outbreaks. Your nitrates are ok. A question I have regarding your loss of fish is did you take them out when dead or did they disappear. If they just went missing that could have a lot to do with excess nutrient and organics in the water as well as your feeding. Decomp. One cube of the food you took a pic of is way to much for two fish. They will not eat it all and it will lead to more of the same problem. Are you sure you found an Emerald Crab or could you have found a different one like a gorilla crab which would decapitate your sea hare. what typeof lighting do you have? Some solutions for the relief of the hair algae is another sea hare, turbo snails and rabbitfish. However, unless you get the PO4 under control it will just grow back. There is also chemical solutions as well. Red Sea NO3/PO4X is a good one and there are others too. You can also think of a refugium in your sump if it will support it. The good macroalgaes will out compete the nuisance algaes for the excess nutrients in the water and starve off the HA and the Cyano (red slime) which is not algae but a bacteria. And lastly, for the bristleworms, there are fish that will pick on them and some crustaceans will feed on them as well. Arrow crabs and coral banded shrimps are a couple that come to mind. bristleworms are also beneficial as they eat detritus and stir up the sandbed. Hope you find this info helpful and good luck getting it under control. Keep up with the water changes and good you got your skimmer up to snuff. Keep it clean including the neck where all the smelly crap settles
