Lonely blue oranda?

I'm writing again about the blue oranda I acquired from my parents. I have him in my 28G planted tank. I had purchased a small orange oranda, but it passed yesterday after I had him/her for 2 weeks.

I had treated and am continuing to treat the tank with flubenzadole which I read (in one of Lupin's posts) is equivalent to Praziquantel. Water parameters are fine. T= 75F, NH3=NO2=0 ppm, NO3 = trace.

However, both before and after I added the new oranda, the blue oranda has been hanging out quietly at the bottom of the tank. He does have plenty of interest in food and eating, and does not show any signs of distress (no clamped fins or gasping gills), but he clearly isn't happy. He did show some interest in hanging with the new fish before it passed, but he was no where near as active as he used to be.

Is it possible that the loss of his two long-time goldfish friends (which passed when he was at my parents' house) is still an issue for him?

I'm wondering again whether to add a new tankmate or to try to rehome him where he can have more than one new tankmate.

When I got the orange oranda that just passed, I got him from a different LFS than I usually use. The tank maintenance and fish health at the store seems very good, but I have lost almost every creature I have bought there within days after its purchase. The orange oranda is the longest lasting survivor with the exception of 4 amano shrimp (of which only 1 remains- though 1 of the 3 that died was an escapee- the amano are not with the goldfish, BTW). I've lost 6 nerites (both zebra and red spotted- in two different purchases as well as 9 harlequin rasboras).

This time, I'm going to go to a different LFS from which I have had only 1 or 2 short term casualties to get his new tankmate. I'm going to try to get one that is a little bigger than the orange one was, and maybe more outgoing to see if it helps my blue oranda accept him.

Well- I bought two young goldies at the LFS. I couldn't choose between the two and I thought that the interaction between the babies might help bring my older oranda out of its shell. I chose a red-capped oranda and a black/bronze-colored telescope goldfish (not sure yet what this color is called). Both came up the glass, when I watched them in their tanks at the store- curiously investigating my presence.

When I released them in their new tank at home, they immediately began exploring- and after a bit, this did seem to encourage my blue oranda to be a bit more active than he has been since he lost his buddies. I'm hoping he'll improve even more as time goes on.

I now it is stretching my space at the moment, but the two babies are pretty small and I can consider other options as they grow. I do think that adding the 2 has made all 3 more comfortable very quickly.

I do have good filtration- right now I have 2 Penguin 150 biowheels and I am going to swap to a 2217 Eheim canister over the weekend.

I have a 75, 2-120s and a 29G. That's what I meant by having some other options as they grow. Based on an earlier thread, I thought that 2 would be okay in the 28G. I know the third is pushing it, but I thought I'd be okay for a little while.