TL;DR
A purchase pool warning means CoinTracking cannot find a prior purchase for a coin you sold. This results in a 0-cost basis, inflating your gains and affecting tax accuracy.
What Is the Purchase Pool?
It tracks your remaining coin holdings based on all recorded buys and sells.
When selling more than you’ve "purchased" (per your selected accounting method), CoinTracking assumes a purchase at 0 GBP/USD, triggering a warning.
Why Do These Warnings Appear?
Missing purchases or incomplete imports
Wrong timestamps (e.g. purchases dated after the sale)
Transfers not marked as “Transfer”
Margin/derivatives misclassified
One-sided tracking (e.g. only importing Exchange B, but not Exchange A where the purchase occurred)
How to Fix It
Ensure all trades, deposits, and withdrawals are imported for all your wallets/exchanges.
Use the correct transaction types, especially for internal transfers.
Check timestamps and time zones on your entries.
Audit balances with the tools under Balance by Exchange.
Example
You bought 1 BTC on Exchange A, sold it on Exchange B, but only imported data from Exchange B. CoinTracking sees no purchase → assumes a buy at £0 → shows a warning and high gain.