I can only repeat and second what has been said. There is NO readily available plec other than otocinclus that is suitable for 30l tank. If the LFS told you the plec was a dwarf then they are pulling a fast one.
Is this the same plec you originally bought or did you replace that with this so called 'dwarf bristlenose'? As that plec was not even a bristlie it was a common and the only way that will be a dwarf is if you keep it in a 30l tank until it dies a horrible painful stunted death.
Your best option is return the plec and put the betta back in the 30l tank which is fine for him.
Is this the same plec you originally bought or did you replace that with this so called 'dwarf bristlenose'? As that plec was not even a bristlie it was a common and the only way that will be a dwarf is if you keep it in a 30l tank until it dies a horrible painful stunted death.
Your best option is return the plec and put the betta back in the 30l tank which is fine for him.
/www.onlinepetsupplies.uk.com/p/7151...m-15-litre.html
WHY IS THIS ONE AWFUL NOW???