From the photo, this is definitely a goniopora, not an alveopora. At least the LFS got that right.
I agree, goniopora are definitely harder to keep, but apparently not impossible. Five years ago I purchased what I was told was an Alveopora, only to realize later that it was a Goniopora... I didn't know the difference at the time of purchase. Gorgeous coral, but everything I read told me it was doomed to die within 8-12 months (or sooner). Nobody knew what it needed in terms of nutrition, and even lighting and flow recommendations were pretty vague. There was, however, the occasional success story (2 years +).
Mine is purple, and baseball-sized when closed. I've had this coral in 3 different tanks. It spent a year in the first, situated 2/3 of the way up in a 46g bowfront tank, but then my tomato clown suddenly took to it and tried to make it his home. The Goni didn't care for that. It then found a home in my sps tank, but even in the quietest areas, the flow was too great, and I think the MH lighting was a little intense for it even on the bottom. After about 6 months, it refused to open, and a few weeks later, I finally moved it to the bottom of my 56g column tank (19-20" below water surface), in a fairly quiet area, under 196w pc lighting, and it has been there ever since (3-1/2 years). It spends probably 90% of its time with polyps extended, making it pretty close to volleyball size (but not quite, and I can't think of a common sphere that matches the size). With polyps extended, it pretty much triples in size.
My Goniopora has spent periods of a couple of weeks closed for unknown reasons, and then opened up and remained so for months at a time. I feed this tank DT's phyto plankton once a week, at about half the recommended amount. The fish get flakes and mysis. I don't really target feed the Goni, but I when I add the phyto, I add it all around the Goni and let it disperse from there. I do 25% water changes with a good quality reef salt mix at least every 2 weeks. It does periodically close up and then reopen, and it does not like to be bothered by fish or inverts. It does not seem to mind small fish like fairy wrasses occasionally swimming through its tentacles. I do believe that it needs a relatively high calcium and alkalinity level, so I recommend a high quality reef salt (plain Instant Ocean would not be recommended, but Reef Crystals would be OK.) I've used several reef salts in this tank over the years, including RC, Seachem Reef Salt, Tropic Marin Reef, and Crystal Sea Marine Mix. I believe the Seachem Reef and Crystal Sea salts have been the best for this tank - the Seachem does have a very high Ca content, so keep that in mind.
There have been some suggestions that oyster eggs are a very good food for these (and many other) corals. I have not tried them because they are incredibly pricey around here, but it's on my list of things to try. Goniopora definitely do consume some phyto plankton. I do NOT believe nitrates are a large issue for these corals. They are native to turbid waters and tide pools, and the nitrates in my Goni's tank are always between 5 and 10 ppm. They may actually require some nitrate to remain healthy. I don't believe anybody really knows what they look like when they are thriving, and they grow very slowly with dense skeletons, so you're unlikely to notice any changes in growth rate. Keep an eye on the polyps along the margin - that's where you will see new polyps forming or existing polyps receding.
Anyway, I think you (the OP) are doing the right things. You strike me as a conscientious reefer, so the coral is better in your hands than in those of your LFS. Keep reading, practicing good husbandry, and checking your parameters. Definitely keep a close watch on the pH and Ca and alkalinity levels and adjust to keep them steady. I recommend the IO alk test - very simple and accurate.
Best of luck to you. It definitely can be done.