Scoping out a tank upgrade

I've had a 125g mixed reef tank running for about two years now. I made some mistakes setting up the tank to begin with, some more correctable than others, and now find myself thinking that I need a larger tank. Therefore I am looking to correct any and all mistakes I made before and try not to make any novel ones this time around.

The theme of the tank was supposed to be Indo-Pacific venomous. I have a Ph.D. in toxicology, so I have a thing for venomous animals (and people confusing venomous with poisonous is a big pet peeve of mine). What I had planned was a P. volitans, another Pterois, either antennata or radiata, and a Siganus magnifica. The volitans and the magnifica were easy enough to get ahold of. The other lion proved difficult enough that I scrapped the 'totally venomous' idea and at least went with 'it can hurt you' by getting a desjardini tang. I added some mushrooms, zooanthids, GSP and eventually started playing around with gonioporas.

At some point, for a period of a few months, I had some personal issues that led to my not taking care of the tank as well as I should have, and the result has been an explosion of algae. I think it is derbesia. Neither the tang nor the rabbit will eat it. I have tried sea hares (all three have disappeared), emerald crabs (added extra to account for predation by the lion, I spotted one yesterday so they aren't all eaten) and a couple urchins, but there is just no way they can take care of the algae, even with me physically pulling out lots with each water change. In addition the volitans is now full grown (I think my avatar picture was from a year ago, and he has grown some since) and is potentially showing signs of stress, that he is cramped.

I live in a 50-year old split-level house. The tank is presently on the lowest level, in what we use as the family room. The floor is tile and that portion is on a concrete slab, so I expect that it can hold a fair amount of weight. I set up the tank too close to the wall - there is about six inches back there, not enough room to get behind the tank if needed. I have an MRC MR-3 skimmer with dual Becketts that is set up to the right of the tank in full view, as it is too tall to fit underneath and there is not enough room behind the tank to place it there. Not that I painted the back of the tank anyway. Did I mention I made uncorrectable mistakes the first time around?

So I started looking at what my options were for an upgrade. I first considered a 180, then realized that a 210 or 220 would have the same footprint, just be taller, and give the fish more room. I have a 72" Current MH fixture, so wanted to stay with a 6' tank, but realized that I could suspend it if needed. I've been bouncing ideas off my LFS, who is great guy. He's one of those folks who will not sell an animal to someone whom he does not think is capable of taking care of it. Probably why, in part, he is now only sellling corals and inverts. He asked for quotes from his suppliers on AGA and Perfecto tanks. He's the biggest Elos retailer in the area, but I know those tanks are way out of my price range. I'm looking to spend maybe $2,000 or so for the tank + stand + incidentals (LR, sand, tubing and the like). I will be re-using the skimmer, lights and pumps from the 125.

I lusted for the Marineland 300DD, but knew that it was out of that price range. Not by a whole lot, but enough. But the 250DD... It is 60"x36"x27". Shorter than my lights, but I can suspend them, and would probably want to anyway to get more coverage in the tank. At 36" wide that is plenty of room for the volitans to swim around. And it would give me enough room for 2-3 more fish. I'm thinking of just toughing it out and waiting to get a radiata, as well as a Parupeneus cyclostomus (yellowsaddle goatfish). I'm tempted to get a Rhinopias, but I fear it would be harassed by the rabbit and the tang.

At this point my LFS is trying to get a response from his Marineland supplier about pricing for a 250DD and stand.