Bleach: Dilute?

[Shells85]

Hi!
Thank you in advance for answering my query. There is varying advice on how to bleach shells in terms of straight bleach or diluted. One expert said do not dilute bleach others say dilute. and how long. We just have not valuable beach collected shells but they smell a bit and they need to be cleaned. If we use straight bleach overnight would that ruin them?
Thank you

[paul monfils]

Most shells can withstand straight bleach without damage, though it should be diluted for some particularly delicate shells. However, in my experience using straight bleach is wasteful because even the toughest cleaning jobs can be done using 25% bleach solution (1 part bleach to 3 parts water).

[Shells85]

Thank you for taking time to answer my query. The information about the diluted mixture is very useful.

[larry.shone]

I watched a video posted by WWM and it showed the use of undiluted bleach. I'm a beginner myself and I have only used bleach diluted, but I have not had any heavily coated shells yet.
Also what about thin bleach, which is cheaper than usual domestic bleach. I assume it is already diluted, but I wonder about the ratio...