Quite to the contrary, unless you use the Tetenal kit at 48C, it is recommended for multiple use even in their booklet, and given its price tag anything but multiple reuse would not be economical. This is especially true for hand inversion tanks where 250ml are required for an 135 roll and even 500ml are needed for an 120 roll. Also note, that even if BLIX gradually attacks its fixer, a trace of extra fixer is certainly not going to hurt, apart from that I wash with water between Agfa 304 stop bath and BLIX.

I have just finished processing two rolls of film with Agfa 304 used as stop bath and just from looking at the negs on the spindles I would say that everything looks normal. Scanning and especially RA4 printing will show whether I got uncorrectable color casts, but to be honest, I doubt it.

There are a few issues with Agfa 304 which may reduce its suitability as C41 stop bath: its relatively low sulfite content and its poor buffering. Note that Sodium Metabisulfite does buffer, but most strongly between pH 6.5 and 7.5, and 20 g/l are not only a weak buffer, but may not even provide enough SO32- for properly scavenging remaining CD-4. I will perform some pH measurements to see whether buffering is at least adequate, i.e. whether pH stays below 5.5 after 5 film rolls in 1/2 liter. In future tests I may end up trying a modification of my recipe: 200 g/l Sodium Thiosulfate, 50 g/l Ammonium Chloride, 50 g/l Sodium Sulfite, Acetic Acid ---> pH 4.5. Or maybe just throw more Sodium Metabisulfite into the mix and be done with it ....