Thought you might like this photo I found on the web. Note, this is not mine. But I did think it warranted discussion for those of you who might be so inclined as to try growing cacti hydroponically.
or maybe even this........
Anne are you growing with water + nutes or some kind of tissue culture medium?
water and 7-7-7.....
I like to grow as well.
Good to see you Warayurt. I don't grow cacti hydroponically. I do grow cacti via bog-ponics though sometimes. I use dirt mixed with bone meal, blood meal, a light dose of fish emulsion and then I set my cacti in roughly 2 inches of water in those dirt containers. Algae often forms while they sit in their wet bogs and at the highest level you can often see the water atop the soil in many of my starter trays or containers. At least for the first few days. I let the level naturally lower over a few days and keep 5 gallon buckets of water available for a quick refill in the green house itself. Everyone has their own madness when it comes to growing and mine is continually evolving or at least I'd like to think so.
More pictures of cacti growing on their own roots in water. There is no go between grafted Pereskiopsis here making this easier. Just the natural cacti with its own roots.