Algae in a pond can be a real pain! Especially in new ponds as you wait for the ecosystem to find its balance.Sometimes the water turns green due to single celled algae. While other times its the string or hair algae that is a problem.
If green water is your problem the solution is more nitrogen processing bacteria. The best and most natural way I find to achieve this is adding in a bog filter. Bog filters are cheap and easy to make yourself. Ive made quite a few and this playlist will help you build one yourself    • OZPOND DIY POND FILTER VIDEOS  
If string algae is giving you grief and you live in Australia, I've found diatomix from algaenviro to be quite effective. If you want to give it a try you can visit their website https://algaenviro.com.au/gardenponds/ and if you use the code ozponds you will get free shipping.
If you don't live in Australia you could try nualgai https://amzn.to/3gTrt4f (amazon affiliate link). It also promotes the growth of diatoms to outcompete problem algae.