They usually only need done if they are noticeably bad, you can usually tell by pumping the brakes and if they feel like they're raising and not smooth I would get it done, $350 seems like a lot though last time I had it done it cost $185 incl. new pads.
I agree with what Sam says but I have also heard that dosing excel aswell as co2 brings certain benefits as it helps the plants utilize the co2 from the diy. Also 120ltr is pretty big for diy co2 so I would keep dosing it to make up for the lack of co2 from the diy.
I always thought the reason saltwater jellies are kept in round tanks is because they need the centrifugal force to keep them moving because if they don't they will die?
I am pretty sure you are the only person on this forum to have them Massey, sort of a pioneer lol. So you're the expert we should be asking for advice.
Thanks Joe, he's got an awesome personality - always tries to attack me when I do maintenance or take a photo. I'm thinking he may be a tad too aggressive to put in one of my community tanks any time soon though lol, guess I'll just keep him busy breeding haha.