I used this. But if I remember correctly when I looked into it anything 30+ ppm should work. https://www.amazon.com/Bio-Silver-Ultra-Colloidal-Silver-Spray/dp/B003LUUMFY/ref=sxts_rp_s_a_1_0?content-id=amzn1.sym.3c8dfbac-8741-40f7-ac26-702635b84b32%3Aamzn1.sym.3c8dfbac-8741-40f7-ac26-702635b84b32&crid=17KDXHUXPDRS7&cv_ct_cx=colloid...
I use this stuff, spray 1 or 2 weeks before it flowers ( usually I do it right at preflower) spray one or however many branches you want to reverse every night for about 2 to 3 weeks or until you see balls. Then voila, you can take the pollen and spread in certain branches or the whole plant. I will say with autos you MAY have to let it go longer than normal so the seeds have time to mature.
This is what I use cheap and works great! Lasts a good while too. I've used this one bottle to femenize 2 branches on about 5 plants so far and its still 1/3 filled up. I'll say too it's so strong when I got half way I topped it off with water and it still works great!
Here is the link to what I am using:
"Bio-Silver" Ultra Colloidal Silver Spray, 240 ppm, 2 oz (59.14 ml) https://www.amazon.com/dp/B003LUUMFY/ref=cm_sw_r_cp_api_glt_fabc_2YYGWZF3ND0F17PARFRE?_encoding=UTF8&psc=1
240ppm is way more than you need. I have diluted this down to about 100ppm, which actually may still be overkill. But it’s working wonderfully so far.
I’ll know more in about 90 days when this Auto is chopped and I do the first run of these seeds.
https://www.amazon.com/dp/B003LUUMFY?ref=ppx_pop_mob_ap_share
Hope that worked. I use this stuff and I only spray the branches I need once a night everyday until I see male flowers. I even used maybe 1/3 of the bottle topped it off with water and it still works great lmao