need help with A6S balls

If your group has cleared this, if possible could you tell me what iLvl their people were when they cleared, what is the party make up, exactly what damage reduction spells were used and what were the tanks doing.
Our party make up is AST, WHM, PLD, WAR, NIN, MCH, BLM, DRG. Everyone is in iLvl 230 at least (some with some iLvl 240 pieces).
At random intervals the tanks either get 1 hit killed by a tank buster, or die from full health at balls. Obviously that is not intended. Hence why I'm asking how to stop this.

My first group was mid 220s in terms of ilevel when we cleared. Our composition was DRK, WAR, WHM, SCH, MNK, DRG, MCH, and BLM. My second group was around ilevel 225-230 with a composition of DRK, WAR, WHM, SCH, NIN, DRG, MCH, SMN when we cleared.

It sounds to me like tanks aren't cycling cooldowns properly or heals are struggling to keep up... or possibly a bit of both. The busters and balls do quite a bit of damage, so it's pretty important to have them topped off, even if they're just missing around 10-15% of their HP. Shields on tanks are also pretty important for the busters and balls-- things like Adlo, Stoneskin if you can, etc. I haven't run this as AST/WHM, but I would imagine a Noct Stance AST's Aspected Benefic could help quite a bit with it.

As a WHM, since I've run it more as that than as SCH, I am usually the one baiting the Double Drill middle, and toss out things such as Medica II when it's needed. I usually save Tetra for emergencies, like if there is a Single Drill and someone is looking particularly low on HP or a tank buster/tank orb is incoming and a tank is needing a quick heal. I try to keep Stoneskin on the tanks as much as I can, but usually when the AoE orbs hit, I leave the shielding for tanks to the SCH and focus on topping everyone up. I don't have a tank cooldown rotation from my tanks available at the moment.

My group was ilvl 221-223.
DRK, WAR, NIN, MCH, MNK,SMN, WHM,SCH.
If tank gets 1 shotted by arm he still has the debuff from the boss, so the OT will deal with the first ones. Tank buster needs mitigation/cooldowns. You wanna do the double buster with 2 tanks when orbs are out, but obviously share them while hes outside his barrier. The ot do some cooldown on the first sets of orbs while me would adlo him, since you have ast you need to give him the shield buff (the heal shield). There are times buster/double buster will happen when a ot or mt tank orb so need to heal them asap. Usuauly the orb thats gonna hit mid, means there will be a tank buster or a double buster, make sure both tanks are top on HP.