Hey Lindalm, I'm in the same predicament as you. My tank isn't as old as yours, and it's a 55 instead of a 38, but it seems my tank won't let more than two fish live in it at any one time. I have all types of inverts (emarald crabs, sally lightfoot, CBS, green brittle, and various hermits and snails), plus a Puffer, chromis, and a SFE. They all seem pretty happy, eat well, and enjoy their surroundings. Over the last month and a half, I've tried to add a Xmas wrasse, royal gramma, and a maroon clown (not at the same time, tried the next fish after the previous one died), and I did the same as you - drip acclimated them in a seperate box for 3+ hours. They would last 3 - 5 days, then I'd find them dead at the bottom of the tank. All my major levels are fine, and I've been doing a 10% water change bi-weekly using RO water aereated for at least 24 hours. The wrasse came from an online store, and the gramma and clown came from two different LFS's in my area. The clown did end up being diseased (Brookynella), but the gramma seemed fine. The LFS said they had it in their tank for a week prior to me buying it. So if you can figure out why your tank can't take on another fish, let me know. I'm not spending anymore money on livestock until I can find some answers.