Interesting strategy that sounds like it should work.

Just out of interest, I backtested your strategy. Using historical closing price data for ETH, LTC & ZEC, starting with a balance of 0.25 BTC in each coin and running from 1/1/18 to today.

The results are interesting, and not as good as expected

Total Value went from 0.75 to 0.799 with this strategy over the test period. However just buying those coins and doing nothing with them gave an end value of 0.776 - so your strategy only outperformed the market by 3% over nearly 4 months.

I may have missed something as I just threw it together, but it looks correct to me.

Interested in what real world returns you are seeing.