Generally fibre aids with D or C, were you drinking enough water with your fibre supplements when you were taking them?
psyllium is a better form to take, easier on the system and effective at the same time...with the fact that you're probably dealing with D from your UC then a bulking fibre is best (Insoluble fibre).
If you have fibre in your diet on a regular basis then you might not find it necessary to use fibre supplements, that is if yu can pretty much guarantee you'll be alb eot eat some form of fire every single day....if not then a fibre supplement daily and indefinitely (flaring or not) is a good idea, that's what I've been taking for the last 5ish yrs and I'm able to eat all fibreous foods without getting bloated/gassy.
You don't have to take your probiotic with your fibre supplements, infact, it's better if you take your probiotics on an empty stomach (first thing in the am/day before you eat).
I take my fibre supplement right before bed every night, with plenty of water.
1/2 tsp to start with is fine, it's always best to start with a small amount and increase only if necessary and after your system adjusts to the initial amount as it may cause increased gas/bloating which is normal and happens to healthy people so just stick with it so your system can adjust to it. that seems to be a big reason why people don't stick with it, the adjusting period can be uncomfortable, but it's well worth it.
:)