NJH

Waveydavey,
Havent fished the canal for 18 months but it wont have changed that much, prior to that i fished it for years and years.
I think if you specifically target tench you may come unstuck. A good all round mix for the gloster would be 50/50 supermatch & supercup (this was Kim Milsoms usual mix).
If you are sure about these tench throw some expo in (if you can find it in any shops these days). Avoid fishmeal though as you will put the roach off and you will need all the fish you can.

Use casters in and squatts you could also suffocate some pinkies but using anything lively will be lost in the silt. Keep this in mind with your hookbaits on the feeder as well and twitch the bait a little.

If you are on the cinema stretch there are plently of skimmers on the pole line or gb feeder 1/2 way to 3/4 across (always try a couple of white squatts on the hook). Cinema stretch is deep, make sure you make your rigs with plenty of line on them.

I have had some good roach catches with a open end feeder with liquidized bread and punch on the hook, fished against the far bank at cinema but september may be a bit early for that.

If you are on the castle stretch take some hemp and tares and feed a pole line at about 8 to 9m.

Let me know what other sections are in and i tell you what i know.

Cheers for now

NIck