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I’m trying to get a clear, bright blue copper sulfate solution for a crystal growing project, but mine keeps coming out with a faint cloudy precipitate after filtering. I used distilled water and heated it to dissolve the pentahydrate crystals completely, but this haze forms as it cools. I’m wondering if my starting material has impurities or if I’m missing a simple step in the purification process.

I ran into that myself last winter. dissolved warm, poured into a clean bottle, and next day it looked milky. seemed like tiny copper sulfate crystals in suspension after cooling. not necessarily impurity, just the solution saturating.

Could be the pentahydrate batch itself came with a bit of grit or mineral traces from the factory. I tried a different brand once and the clouding dropped, but it didn't vanish entirely.

I once blamed the filtration, thinking the paper added something, but the haze popped back after a few hours regardless. Maybe the issue is how quickly it cools or the concentration sitting at the edge of saturation.

Would you test by letting a small portion sit at a constant warm temp to see if it clears or stays cloudy?

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