You might be growing them at acidic pH. So you can dilute them with water to bring conductivity below 5 mS/cm and load on cation exchange resin. Or you can increase its pH to 9 with tris Base and Load on the any anion exchange resin. For more Purity you can Load the elute of the ion exchange on HIC resin. If you dont want to go for Ion exchange resin then you can do precipitation by pH or any salt to remove impurities.
We add a 6His tag and then isolate the protein from the growth media using a Ni or Co column. Other options include, depending on the size and solubility of the protein (and volume that you are working with), a filter concentrator with a MWCO smaller than your protein or ammonium sulfate precipitation.