You should count your gains in eth instead of fiat, eth is relatively stable and fluctuations in eth affect the valuation of all altcoins, just like btc. If you really need to count in USD you can sign up for bitfinex in a few days, they use USDT.
ETH is stable?? ETH went up 100% the last 10 days.. :-)
Thats not what "stable" means.
Binance where I am, has also USTD. But you cannot buy altcoins (or set a buy limit) directly from USTD. At first, one have to change USTD in ETH (or BTC) and then it is possible to buy altcoins.
I think in bitfinex will be the same (?)