I use to have a beckett skimmer that I made. I first tried with a mag12 performance was so so. I then put a genx40 then a genx55. Wow this thing would suck some serious air. With the genx55 with two inj I could pull over 20 LPM each. The skimmer was so hard to control it wouldn't work right. If I adj air valve down to 10 it was ok but bubble size was still a problem. Skimmer was 10" around by 36" tall. The pump was too loud, it's in the tv room so I got a sedra 9000. The 9000 pulls 9-12 LPM it's not modded. It works pretty good. The skimmer is too tall to fit my future plans and I have started a prop systen in the garage. So I built another skimmer. This time I'm useing a defuser, 10" around and it's 30" tall. A friend had a muzzi inj so I put that on with the mag12. I get 15-20 LPM, bubble size is pretty good. Soon here I'll get the mesh and mod 9000 and a quietone 4000. After that I'll try the becckets again and maybe I'll try to add the two. Inj a modded quietone 4000, I think the 4000 won't spin with all the air. It won't cost me anything.
Titoreefs, beckets can be a pain to adj. Try to adj air valve, it sounds like it's open too much.It helps to have the water line fixed where the skimmer is. Adj the water line in skimmer to where just a little bit of bubbles exit.Then adj air, only a little at first and wait 12 hours. Adj as needed. If the skimmer goes flat there isn't much to skim.You mite want to clean inj and pump. I adj mine about 6" from top. I hope this helps ya.