A purchase pool is the remaining sum of a coin, added to with purchases and reduced by sales.
These warning messages appear on the "Realized and Unrealized Gains" page as well as in the "Tax-Report" for every time you made a sale, but the purchase pool was already empty (according to FIFO or any other selected method). This is a sign that transactions are missing in your account.
Either they were not imported correctly, or you forgot to add them into your account. It's not possible to sell coins you did not purchase before. Subsequently, the calculations for the gains and related numbers are wrong.
Other common reasons for the warnings are incorrect entries, wrong time stamps, and margin trades.
Please make sure you have entered all transactions (deposits, withdrawals and trades) for all exchanges you've added to our system. Otherwise, the balance will not be even, and the calculations will be misleading.
The most common reasons are that you bought cryptocurrencies on an exchange that is not in our system or that you did not record the transfer.
So if you bought 1 BTC on "Exchange A" and you sold it on "Exchange B", but only "Exchange B" is tracked with our software, there is no chance for us to calculate gains, taxes, etc., we need to assume a purchase on the same day for 0 USD.