This is long, sorry all. I’m just so upset. My two beloved clownfish, Trick and Treat (we got them Halloween 2016), have both died suddenly tonight and I am heartbroken and have absolutely no idea what could have happened. Here is all of the info I can think might be relevant. If anyone has any thoughts on what could have caused this, I would very much like to hear. Tank: BioCube 29, set up Sept. 2016 Heater; intank media basket with floss, purigen, and chemipure; MJ1200 pump added a couple of months ago; koralia powerhead added several months ago. Inhabitants: two Wyoming white clownfish were the only fish. The rest: green star polyps, pagoda cup coral, toadstool leather. Edit to add: clove polyps. One skunk cleaner shrimp. Snails: two nassarius, two cerith, two asteria, two trocchus, random stomatella. Random hitchhiker crab I just found this week. Lots of algae. Bryopsis mostly right now. Parameters after the clowns were found dead: Temp: 78 Salinity: 1.025 PH: 8.1 Ammonia: 0 Nitrite: 0 Nitrate: 20 (this has been higher than I would like for about a month) Phosphate: 0 Calcium: 420 Dkh: 11 All other inhabitants seem fine. The corals looked ticked off. But it’s hard to tell because they get sleepy at night and start to close up and they have some algae on them which has been ticking them off (the pagoda cup specifically). The clowns have been acting like their usual silly weird selves. The small one just recently discovered (maybe two weeks ago) that he likes snuggling in the toadstool leather so he’s been doing that a lot, which was adorable. He and the larger clown got along well, but she did try to show him who’s boss once in a while. I never saw any contact aggression, even when they did occasionally squabble. They’ve been eating well, they’ve been swimming normally, they’ve been totally healthy fish as far as I have observed, until I found them dead. This has honestly come out of nowhere that I can see. They were swimming happily a couple of hours before I went to say goodnight to them and they were dead. I haven’t added anything new to the water. I haven’t cleaned up in a while (hence algae) or done a water change this or last week. The filter and heater all seem to be running fine. There were no chemicals/fragrance/sprays in the area at all. No cleaning, no cooking. My little parrot near them seems fine, and my freshwater tank in the same room seems normal. The fish showed no signs of injury. The gills looked a bit puffy but they weren’t when I saw them alive so I think that must have just happened to their bodies when they died? The only things I can think of at the moment are some sort of electrical current? (But the inverts seem fine.) Or one of the corals released a toxin that somehow only affected the fish. This seems the most likely? Edit to add: can algae cause sudden fish death somehow? I’m really sad and confused. I loved these fish so much.