The Zcash nethash has increased crazy amounts in the last 7 days.... my 1 Z9 mini was making .6 coins beginning of the week and now returning .4 coins... There was a slow reduction since I got it in June, but the last 1.5 weeks, the decrease in returns have increased significantly.
Your z9 mini uses algorithm "Equihash" and a number of coins use that algorithm.
If you bought your z9 mini just to mine Zcash(ZEC) and hodl that single coin you are out of luck, I guess.
I, myself, use multiswitching(switching between different coins that all use Equihash algorithm) when mining and in my case have what I mine exchange to Bitcoin(BTC) and Litecoin(LTC) and then I choose to hodl BTC and LTC.
I use prohashing.com as miningpool with nanopool(ZEC into a wallet and autoexchange to BTC) and MPH(Multiswitch and autoexchange to BTC) as backup miningpools.
You can use whichever miningpools you choose.
You can also choose to mine to a wallet/exchange where you yourself can exchange to other coins/Fiat-money (£, $, ) you find attractive or best price.
All info about this can be found in this forum and on the Internet.
Good luck!