What else for this container pond?

As part of my recent garden renovation I have out in a container pond in a belfast sink.

I have put in four plants so far- Red Stemmed Parrots Feather – Myriophyllum

Water forget me not – Myosotis Palustris

Carnation Grass – Carex Panicea

Penny Royal – Mentha Pulegium

I think it could do with one more plant possibly but I am not sure what?

I am also on the fence if I should get a little solar fountain or not?

Anyone got any suggestions for improvement?

It’s located in a south facing flowerbed but it does get shade later in the day due to a garage nearby.