That swing is big enough for me.
Had the same problem and lost a colony or 2 from that swing.
Your tank conditions is basicly the same is mine.
Strugling to get my mg from 1150 to 1300 and my alk is permentantly on 7 for the past 2 months.
How much do you topup each week and what is your topup water's alk?
Top-up is probably 5-8 litres per day .... and I have no idea what the Alk of the top-up RO water is (never thought to test it)