Not sure mate, don't have the money to stay in hotels in Dublin
There are so many to choose from most will be of a good standard as well. You want somewhere city centre, preferably south of the river liffey, southside as opposed to northside of the city, better nighlife southside, pubs restaurants clubs etc. Its hard to tell you where to look exactly, see what you can come up with deals wise and post it up here at least I can tell you if its a good part of the city to stay in. I imagine city center would be best though for shopping sightseeing nightlife etc and general getting around. Leinster rugby club play not to far from the city centre, only a short bus/taxi journey if you were interested in catching any of the home games, Heineken/european cup games in full swing right now, Im sure the GF would love it
Grafton Capital Hotel I presume, Lr Stephen St D2?
Great location, really central in a very good area, perfect really, 5 or 10 minute walk to absolute loads of stuff, Temple bar about 3 mins away, lots of other good pubs restaurants right outside your door. Right beside Grafton St/St Stephens Green shopping centre for shopping, couple of minutes walk to St Stephens Green park/ Trinity College. Great choice of Hotel.
Nothing really that I would go out of my way for tbh. That area is too expensive for pet stores, the shop rental costs would be off the wall around Grafton St area. There is a place near Temple Bar beside the Liffey (on the Quays) called Boardwalk Pets or something like that, but it wont be up to much, few guppys or neons that sort of thing, you won't find any plants worth talking about in that store, not worth a visit tbh.
There is one Store called "Wackers" on Parnell St (behind the ilac shopping center) which is pretty good, not a bad fish section and he usually has Tropica plants in, its expensive though. Probably a 15-20 minute walk from where you will be staying, find your way to the end of O'Connell St (Dublins main Street) take a left at the end of O Connell St and its not too far from there, only a couple of minutes down on the right hand side of the street beside a cab/taxi company. Its probably the best store in the city centre area. I used to go in there quite a lot for plants, when he has a new shipment of plants in it was always worth a visit alright. Most of the best aquatic stores are in the suburbs,there are some very good ones but they are spread all over the place, you would really need a car.