Till now, I have never seen a UG flower underwater, my best guess is it's not able to...
but if the light is sufficient enough it will flower abundantly when grown with the leaves above the waterline. I've seen UG growing and flowering on the window sill in a puddle of water in a small cup with indirect daylight only. I've seen the pictures on the website of 'The Carnivore Girl' but this domain is no longer registered. She grows anything carnivorous she can get her hands on... I know she has a Facebook page with the same name, i guess it will also have the UG pictures.
The Carnivore Girl. 4,448 likes. The Carnivore Girl is an online boutique and blog dedicated to all things carnivorous plants! Click below to check us out!
www.facebook.com
And I remember she stated that Utricularia is tolerant and grows very well with this stuff.
If you are a Facebook member you could try to drop her a message for some advice on UG...
I have grown several UG species emersed myself except UG... But all flowers rather easily and abundantly are not at all difficult to keep if sufficient air humidity is given. I have no experience with the Maxsea fertilizer, I've always used Rhizotonic which is probably similar and also a seaweed extract with an extremely small amount of NPK. Rhizotonic advertises the property of feeding and aiding microbiological life in the substrate. My best guess is, it will also do this in water and that it's this that is most important for Utricularia since this is what it preferably depends on and feeds on after all it's a carnivore.
There will be more brands on the market sold as Root Stimulators for plants that are based on Seaweed extract... But i don't know if they all are the same...