I have a futurebit Apollo miner. Mines at about 3TH.
I bought it about a year and a half ago. Initially it mines about 1,000 sats a day. However, over time it kept going down. As of now it's averaging about 600 sats a day.
Why is it mining less? The halving hasn't happened yet
Also, I have been mining with Braiins pool the entire time, if that makes any difference
It has nothing to do with the halving. The more miners mine, the less shares you'll get. Let's say the total hashrate for mining bitcoin is 1000 th/s in the world and yours is 10 th/s. You get 1% of the total block prize on average. When the total hash rate doubles (2000 th/s) and yours stay at 10 th/s, you'll get 0.5% of the block rewards on average in the long term.
Since there are more and more miners start mining every day, unless you increase your mining power too, you'll always get less satoshis...
For this exact reason mining don't make sense for home miners.