Postgres Database Free Storage Space Downward

I have a situation on my Postgres 13 db on AWS. * 8TB of storage * 60GB of memory that it isn't really using * I regularly check to see if any query is running and if so, kill it. * Transaction Log Disk Usage in blue, replication slot disk usage in orange. * Replication lag is over 500GB behind * FreeStorageSpace is sawtoothing * I combed the logs looking for "timeout", "error", on replication publisher and subscriber in hopes that the wal_sender_timeout and wal_receiver_timeout needed adjustment, however I see nothing. * I see the weird LSN behavior where it advances, the machine runs out of space, and then rewinds as if to start all over again.

-- 3851F/6305C2D0 7:46
-- 38521/3829A280 7:50
-- 38535/9FC44768 8:38
-- 38544/8E82F3D8 9:12
-- 3854F/8BD52F00 9:39pm
-- 38504/9EABBE48 6:29am <- rollover
-- 3851D/9413C9D0 6:11pm

* The amount of data sent between the publisher and subscriber is actually very low when looking at the AWS network sent/received charts. * I actually had 2 subscribers at the beginning. I took the smaller one offline since it's easily repairable. That helped with the storage pressure, but only a tiny bit. Questions: * I don't know for certain that it's the replication that's causing the free space to drop. Is there a way I can verify for certain? * I don't think Postgres 13 has parallel replication from what I saw in some documentation. Is there a way to fake it? * Is dropping the subscription, killing the replication slot on the publisher, truncating the tables on the subscriber, and creating a new subscription my only option here? * Since I have at least 2TB free storage when the drop begins, and the replication is ~500GB, I would think that whatever the publisher has to send would fit in storage. Should I increase storage in hopes that it can overcome the problem? I don't have a sense as to how high it should be increased. Can it be scaled back down after the fact? * Are there any suggestions as to keywords I should look for in the log files? Any responses are greatly appreciated.