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The Skywatcher 72Ed is an ED doublet - it is not apochromatic. Semi-apochromatic at best. Yes, you will get blue bloat with most doublets (some exceptions in exceptionally well corrected systems, but they cost a lot for doublets).
I do hope the dealer you bought it rom did not claim they are apochromatic. Merely having ED elements does NOT an apochromat make, nr does a triplet assure apochromatism (many Chinese triplets are not apochromatic)
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