GSP can definitely take over a tank, but nothing beats Xenia for overtaking a tank; be happy yours are not doing well :)
I’m kind of joking of course, but definitely know that many, many have regretted getting Xenia. I actually really like them, the pulsing (When they do it) is nothing short of cool. But I haven’t found a way to keep them successfully at bay. Even keeping them on a totally separate rock than your main aquascape doesn’t really work, they seem to just show up everywhere in the tank.
I believe that no one knows for sure why or why not they pulse. And even though this is considered an easy, beginner coral, this kind of thing does happen where no matter what you do you just can’t seem to be successful with a particular coral.
That said, not having test kits to test for water parameters is a problem, in my opinion, especially if you’re just getting going in the hobby. I would suggest that you stop acquiring corals, and put some money into some test kits. I believe the Salifert test kits are the best bang for your buck, reasonably affordable, regarded as accurate, and easier to read than something like API where you have to match colors.
https://www.saltwateraquarium.com/s...MIwfLL_6rRiwMVQHBHAR1SAxfjEAQYASABEgLvUfD_BwE
You don’t have to buy them all in one bundle like that, but this would be a good selection of test kits if you want to keep corals.
It’s very hard for anyone on R2R to help you if you can’t let us know what your water parameters are ;-)
This could be your lighting, but also flow is very important, as are your parameters.
Are you using tap water or RODI water?
A little more info may help the R2R gurus better help you.
Good luck!