If you use Rydlyme for cleaning your engine cooling, it works fine in a toilet bowl and doesn't bother any marine metals. It's also biodegradable.
I checked the MSDS for Rydlime, and it is biodegradable...more importantly it's also environmentally safe. Those two terms do not mean the same thing.
"Biodegradable" is a meaningless feel-good term that product mfrs put on product labels to mislead consumers into believing it's environmentally safe...in fact, formaldehyde is only one of several lethal chemicals used in some holding tank products that can legally be labeled "biodegradable." Others include glutaraldehyde and quaternary ammonium compound. They will eventually bio-degrade, but not until they've had plenty of time to do plenty of environmental harm.
The first aid warnings in a product label or MSDS are best indication of whether a product is enviro safe or not. If they say something like "harmful or fatal if swallowed, may cause blindness, call poison control immediately if ingested," that product is no more enviro friendly than a toxic chemical spill. But if they say something like, "if ingested, drink copious amounts of water, flush eyes with clean water for 15 minutes, consult physician if symptoms develop" (which, btw, is close to the first aid instructions in Rydlime's MSDS)...it won't harm you or the environment. Muriatic acid's warnings are bit stronger, requiring a bit more care in handling.
Just something I thought y'all should know....
Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein