Final answer:
Possible causes for slides turning out 'too red' include an incorrect pH level of the stain and over-staining the slides.
Step-by-step explanation:
If the slides you are staining are turning out "too red," two possible causes could be an incorrect pH level of the stain or over-staining the slides. pH is a measure of the acidity or basicity of a solution. If the stain is too acidic, it can cause the red color to appear more intense. Over-staining occurs when the slides are left in the stain for too long, resulting in an excessive amount of dye being absorbed.