Alsta TCH - perhaps one for chemical engineers

One of the things I miss most from back home is Domestos.  To the non-Brits, Domestos is a bleach used mainly for cleaning the toilets and it's a gel so it clings to the bowl for a long time.  I believe that Clorex and Harpic make a similar product in US.

So, a bit of googling on a boring Sunday morning has led me to some Youtube video's on how to make your own.  RO water, check, Hydraulic Acid, check (pool shop), and Alsta TCH - no check.  I can't find out anything about it but it must be commonly available in US because of the number of video instructions - none of these numpties were wearing gloves in the video's, idiots.

So, perhaps Alsta is a brand name, my googling may be going off on a tangent but I can't find it anywhere.

I did come across a really good video to make a small amount of gooey thick bleach to put in a ketchup bottle for cleaning the grout on your tiles, ingredients only water, cornflour and supermarket bought bleach.  Should you be interested, the link is here.

 I would dearly appreciate any help on if it is likely to be available here, what it is called if it goes by a different name and where I might purchase some.