thanks for advice here. Poos were normal for a couple of days but have gone back to soft/tear-drop shaped in last two. Strangely enough it seems to be the days he's on grass that he's straightened out. And the other one's poos were the same last night, I noticed.
Antibiotic was Baytril.
No, I haven't ruled out anal impaction - wouldn't know how to rule it out - do you want to tell me? (It's going to be ick, isn't it.)
The vet saw the poo when we had Mike in for mites and did originally think stress from mites/treatment but he's been sorted out for a couple of weeks now and his poo is still funny. It'll have a day here or there where it seems to be right, then back to being squashy but I cannot pick a pattern.
As I said, most days they're on grass in the day and lucerne at night, although with the crap weather they've been on lucerne 24/7 with a little f&v for brekky and dinner.
what is really giving me a headache is all the conflicting advice - not from you lovely ladies but just in general. I read half a dozen books when we first got the gps but gave up because they were all so contradictory. 
3 vets, including a small animal specialist, have given their blessings for having the boys on lucerne. I wouldn't have a clue where to get the other stuff - in pet shops and the animal produce store, it's the only kind of hay available.
Apart from the days on grass, we did cut the gp's f&v right back after Mike developed an eye thingy - please don't ask me the proper name - a calcification which the vet thought could have been ... supported by an excess of Vit C.
Don't really think the lushness of the grass can be a factor - although it's been pissing down for a couple of weeks now and grass is growing again, he started when we were at the end of a horribly long, hot dry period (I'm in Oz) and the boys had nearly chewed the lawn bare because nothing was growing back.