Softwashing anything is a good example of killing bio films on walls paths etc but that is far greater build up than you will get in an ro system , however once a membrane is clogged up it will need replacing as it’s like a fine gauge sheet tightly rapped up . But hypo will 100% kill anything like that . All water authority’s use hypo to sterilise there filtration plants and kill off bacterial growth , Ime not sure on the frequency of application but they do it on a regular basis . As a side point I flush all our vans tanks with a hypo mix every 12-18 months this kills the slimy feeling on the sides of the tanks that build up over time , especially if you use hot water as this encourages the growth and it multiplies much faster . After flushing the tanks the sides are no longer slippery your hand stickers to the inside of the tank rather than sliding around on it if that makes sense
I've never had to do a van tank, i havn't come across a problem with any growth in a van tank so i can't comment on that. I use Hypo like you and i fully know how good it is at what it does. Like you i assumed it would kill anything like that, but it doesn't.
Here's my experience with filter housings and hypo. The filter housings get a thin film of very light brown slime. I used to just call it gunk, it took me a while to understand it was actually bio film. I can drop the housings in hypo solution ( i did regularly) and it did not remove the slime at all. I had to wash them out with some soapy water and a micro fibre. So in my own experience the hypo did not remove it nor prevent it from coming back. Of course it was only removed from where i could touch and scrub, so it was still there waiting to continue to grow again.
I'll try be brief here as i've a tendency to waffle on
What led me to try this was a friend had a hot tub problem and he asked me for help as he knew i filtered water and may know some stuff. He was getting hot tub rash, had his water tested and had an engineer out to check the system. He was told to chop his hot tub up and skip it as it had a bio film infection in it and you can't remove it. Of course i didn't really know some stuff, i thought i did !! I told him to pop a 25 litre tub of hypo in there and it will kill anything. He'd already done it, and it didn't. His bio film had gone from the smooth surfaces of the hot tub where he could scrub with a cloth, but not gone from the places he could not reach, the hypo did not touch it. Sure enough i done some research and you will find its accepted and stated that Sodium Hypochlorite does not infact remove bio film. I can agree with these findings, as it never removed it from my filter housings either.
A brief google of some of the ingredients of bio film removers will lead you to the same ingredients as bio washing powder. They're designed to remove oil, grease, fats etc... from delicate fabrics at low temperatures. I've tried it and its worked. I'd already bought a replacement membrane so my intention was to replace it but try and cleanse the system out thoroughly before replacing it. If the bio removed crud from the membrane then that was a bonus. It looks right now like its worked. I take your point about a membrane being a fine sheet of stuff and fully understand that. Next clean i'll do a small vid to show, you'd have to see it with your own eyes. But in anycase i can't argue with the results, i seen the dirt come out, i seen the TDS come down and the new membrane is still sat there on the shelf.