Have you had any issues when the water goes greenish over a certain point with your gorgs? When mine hits a certain level they will stay closed for a day or so. I let the glass build up for 2 days, scrap it for additional food, then next day do the water change. If you up the water changes check your ph level again, you might not need the kalk. Besides water changes I also run a small amount of I run a small amount of carbon (FM carbL) to keep the green down.
For salt, I went to Coralife (was using RC). It is good quality, not hard on the pocket when you need to do a lot of water changes, and is easily available locally.
For Dendronephthya, I was able to keep for almost 8 months, then one day they looked like they were melting. I tested everything, I checked my log books to see if I did anything different, checked my RO system, everything that might have been done in my house...couldn't figure it out why. Now I will keep anything non-photo/filter feeders just not them...oh...and not thos Aussie spider sponges either...just a quick way to lose money.
I found that gorgs in nanos seem to do alot better, that may also be the same with Dendronephthya. The turnover & higher concentrations of food getting directly to the corals have been working better than in my 90.
Mike