My bass makes the whole mix pump. What kind of compression fixes that?

Why the low end drives a compressor

Low frequencies need far more level than highs to sound equally loud, so the bass and kick are the largest signals in a mix. A compressor across the whole mix measures the total, and the total is mostly low end. Each bass note pushes it over the threshold, and the vocal, guitars and cymbals are turned down along with the bass. That dip and recovery is the pump.

Fix it at the source

• Compress the bass track so its notes are even before they reach the bus. An even bass gives the bus compressor nothing to react to.
• Tame single notes. One resonant note that jumps out is a job for a dynamic EQ band at that note's frequency.
• Duck the bass under the kick. When both land together their levels add. Lowering the bass a few decibels on each kick removes the biggest peaks.

Fix it on the bus

• Use a multiband compressor. It splits the mix into bands and compresses each separately, so the low band can be held without the mids and highs moving.
• Ask less of the bus compressor. If it shows more than 2 to 3 dB of gain reduction, raise the threshold.

A full-band compressor is the wrong tool here. It is what causes the pump.

In Zammoth

The Multiband Compressor has three bands with their own threshold, ratio and makeup. Its crossovers start at 150 Hz and 2 kHz, so the low band covers the bass and kick as it loads. The Dynamic EQ has up to six bands that act only when their own level crosses a threshold. The Duck device lowers the bass while the kick plays. The engineer's measurements include a flag for over-compression on the master, so it can say whether the pump is coming from there. See the Multiband Compressor reference and how to sidechain the bass to the kick.