Is that this green filamentous slimy stuff? Then it is pretty normal to have it this time of year, especially in a fairly new pond. It's still rather very cool, at least the nights are and also are still relatively long. The mature plants are all still in their premature startup phase, new yet not fully rooted plants are busier with surviving the cool water temperatures and are at a standstill.
I have this slimy stuff each year over again starting from April till the end of May into June, then the plants will start to metabolise at full throttle and the algae will disappear as quick as it came.
I've tried V. spiralis in the past but in my experience, it was still a much too young a plant and rather temperature-sensitive it didn't survive because I planted it too early and could be the fish loved it. I would at least wait another month for the nights to get warmer. Next year once it has a fully developed root system it could be different.
You could try a Potamogeton sp. (natans for example) these are native and pretty strong and will survive mild winters as evergreens and start growing much earlier. Also early growing marginal plants could be of great help, such as the Iris pseudacorus is an extremely early grower and already about mature enough to flower in the month May. The Eriophorum angustifolium is also a relative early starter and would be a great follow up next to Thypa minima. Finding a complete database for pond plants that also gives the flowering month, you can choose plants flowering from early to late in the year. Early flowers mean it needs to start growing early will help startup the pond. Follow-ups that start later keep it up and running and you'll have flowers the entire season. For example Schizostylis flowers very late, and also start to grow later, it will still be about dormant in May but starts growing in the warm summer and flowers in September till November...
Choose the plants wisely regarding this and use their seasonal properties to the full extent..