an iris will take over your pond thow you can take it out in spring and cut some of . id be inclined to get a dwarf lilly and maybe planting around the barrel . it will help a lot of birds so would be worth making a shallow part so they can bathe and drink etc . id forget the pump as you have know fish and put some decent soil for water plants in the bottom .some of the oxyginating plants would d well . all water plants die right back i winter so dont worry .

I don't know who told you that Nymphoides Peltata is a deep water plant because it isn't - should be grown in shallow water at the margin of a pool or pond, as should the iris. You can read the RHS info on it by going to:

http://apps.rhs.org.uk/plantselector/plant?plantid=1343

25 inches in diameter is not really that big the barrel is designed to be a water feature rather than a pond and plants are going to struggle. I wouldn't recommend your getting any fish as the water will get tainted from the whisky impregnated in the barrel.

a dwarf lily hould be fine . its the wildlife you get bye just having a water sauce .

Thanks very much to all who replied. The peltata was labelled deep water plant at the garden centre just goes to show shouldn't believe everything you read! I shall give them a go but plant the peltata higher than I had intended and wait and see. Thks again

most water plants however big they get start of small . thow light penetrates well thew clear water but the spectrums the plants need get filterd out easier than youd imagine . im not very good at latin/flashy names but i do know about pon lants . if there small get them up high to tart with till they grow a bit . then just lower them till they seam happy .