Isn't the essence of your problem that you are trying to calculate off of percentages of a volume per shipment? In other words, shouldn't you store absolute quantities of the components inserted instead of percentages of the received shipment? I.e. from the volume and percentages of a receipt you can easily calculate the absolute quantities of each component and merge those into the quantities already there (very much like the liquids themselves). Calculating the percentages over the contents over the entire tank or a partial shipment taken from it will be an easy task given the volume of the tank/shipment and the absolute quantities in your table.

The only thing that could be of worry if this is a continuous process, are rounding errors. I can imagine that some components are added in very large percentages, whereas others would be inserted in very minor quantities only. Actions like taking shipments from the tank will make rounding errors have a bigger impact. If I were in control I would suggest to periodically empty the entire tank to avoid these rounding errors grow out of control. But if this is a production facility you most likely already do something like this, and thus your software rounding errors will be reset with every cleaning of the tank too.