It will depend on when the info is received from CSA as to how much ftb you lose. The only time that you will know for sure what you are going to lose over the course of the year is at tax time when everything is reconciled. Until then, it is a theoretical

There are two methods of calculation for how CSA payments impact you. The one you were on where you were impacted each and every fortnight is one of them. With that one, there is minimal chance of you being overpaid unless you get arrears or you have a higher assessment come in later in the year.

The other is far more complicated and carries a high risk of overpayment, as you are seeing here. Basically you are only impacted if you receive a payment, and when you do, the system has to correct all the previous fortnights where you weren't impacted by that assessment, and reduce all your future payments to account for the previous overpayments as well. In top of that, the system also assumes that you will receive money for the balance if the financial year so factors all of that in as well.

Honestly, the safest thing for you to do (as much as it sucks for you for right now) is bank the money from CSA. Take from it whatever dollar value you lose from ftb each fortnight, and leave the rest there until reco. Once reco goes through and supplements are processed, the balance is fair play. Until that happens, you have to wear the fact that if you spend it, you may end up worse off in future fortnights. Please note I am saying this is the SAFEST thing to do. I am not saying it is the only thing. I am a realist. I know it will be next to impossible given other threads you have posted. Perhaps you could work out how much ftb you are due to get for the next half dozen fortnights (til end of fin year) and put that aside as "worst case" with you having payment reduced that drastically - and then the rest can help at the moment....