How do I create a transparent liquid for ferrofluid display? Hello~ I am a media art artists working in Korea.
Recently, create a kinetic artwork using ferrofluid.
I need to create an artificial pond with a diameter of 3 meters. So I need a lot of suspension liquid.

Prototyping
https://youtu.be/3o33upltO34

simulation videos
https://youtu.be/NE19B_2byGA

Unfortunately, I tried my solution failed.
- case 1: Deionized water 40% / isopropyl alcohol 40% / Propylene Glycol 20% (Stains occur on the glass )
- case 2: Deionized water 60% / Coco betaine surfactants 40% ( no stain but, This seems strange movements)
- case 3: Deionized water 35% / isopropyl alcohol 35% / Coco betaine surfactants 30% (Stains the glass )
- case 4: Deionized water 60% / LES surfactants 40% ( no stain but, This seems strange movements.)
- case 5: Deionized water 60% / APG surfactants 40% ( no stain but, Decomposed into many particles)
- case 6: Windex(Glass Cleaner) 100%  ( no stain but, Decomposed into many particles)  

I used glass types
- pyrex glass (Small stains occur)
- tempered glass (Small stains occur)
- soda-lime glass (Big stains occur)  

I was always cleaning solution into a container before adding the alcohol.

And most it had hardened over time, the ferrofluid.
There's a really good video on YouTube by Nilered/Nileblue on ferrofluids. In it he suspends magnitite with oleic acid (main component of olive oil) as a surfactant and uses Kerosene (Paraffin Oil) as a carrier.
There's a PTFE 'dry lubricant' sold under the WD-40 brand name that might be able to prevent the glass from staining as it creates a thin coat of PTFE on the glass which is highly inert. Just spray the piece of glass with the PTFE Spray and wait for it to dry (~7mins). [The PTFE spray has a myriad of other uses too, you can put it on any surface you want to have low friction, to be lubricated, an unreactive surface, dust repellant surface, etc].
This might be a way around the staining issue you are getting. Or at least point you in the right direction. Good luck!