Bittrex will be removing orders that are older than 28 days.

Bittrex is committed to providing fair and efficient price discovery and these changes are designed to improve the overall trading experience on our markets.

Removing stale orders:  Effective today, Bittrex will be removing orders that are older than 28 days.  As we’ve communicated in the past, many of these orders have no reasonable expectation of being filled and clog the order books. 

Raising the minimum trade size:  Within the next 2 weeks, the minimum trade value for orders will go from 50,000 Satoshis to 100,000 Satoshis.  We will also require a minimum trade quantity.  For example, DOGE trades at 22 satoshis.  The minimum trade quantity is 4500 DOGE and the minimum trade value is 100000 satoshis.  The smallest order in the book is 100000 DOGE at 1 satoshi each.  The largest order in the book is 4500 DOGE at 2 btc each. 

Creating minimum tick sizes: Within the next 2 weeks, on a per market basis, we will be instituting minimum tick sizes that are based on the current price of the market.  The target is to have minimum trade sizes that are near 0.1% of the current price.  The current minimum tick size is 1 satoshi.  For example, Ethereum trades at 0.0577 Bitcoin.  Bids and asks can only be placed in 0.0001 increments.  So the next level on the bid side of the orderbook will be 0.0576 and 0.0578 on the ask.

A general statement about market manipulation tactics:  Bittrex actively discourages any type of market manipulation, including pump groups.  Consistent with our terms of service, we will suspend and close any accounts engaging in this type of activity and notify the appropriate authorities.  

source:  https://support.bittrex.com/hc/en-us/articles/115003004171