Use Hexane/Ethyl acetate. If your compound is polar, you can even use MeOH+ EtOAc to elute. 

Try tetrahydrofurane /THF/ or acetonitrile, both pro analysis purity. As for your chloroform/ethanol mixture, test it for contaminants by GLC.

Prior to purrification of trialkylated triazolealdehyde use longer column, wash it with the chosen solvent, and try to check the column leaving solvent for impurities. You may find and use also more specific fillings with higher adsorbing activity.

 R.S.

Depending on the nature of your aldehyde it may be worth trying to avoid alcohol based solvent system. More electrophilic substrates have a tendency to form acetals and hemiacetals as the silica can act as a mild lewis acid/dehydrating agent which can complicate purification. This can be ameliorated by adding a drop of triethylamine to the column solvent or switching stationary phases to alumina. Caution is advised as aldehydes can be quite sensitive to acidity and basicity.

Determining solvent systems is often a matter of trial and error, run a TLC analysis on the impure material with a variety of different solvent systems, look for a desired Rf of ~0.3 which gives good separation of impurities. Try a broad range of dissimilar solvents, mixing non-polar with polar, for non polar you can use hexane, toluene or dichloromethane. For polar solvents ethyl acetate, diethyl ether, acetonitrile, acetone etc.

Depending on the Rf of your triazole. In my experience, triazole groups are quite polar and they present very low Rf values with silica. In addition, if your triazole bears an aldehyde, I agree you should first deactivate the silica gel column with triethylamine and then try to use Ethyl Acetate or 1-10% of Methanol in Ethyl Acetate (v/v). Check with the aid of TLC analysis. 

What would be the best solvent for purifying piperonal?