Posted: Sun Sep 19, 2021 8:19pm
The first thing you are going to need to invest in are some test strips. This will help you understand what the chemical situation is in your pool.
Do you have a regular chlorine pool or a saltwater system, you didn't say, but I am guessing you do not have a saltwater pool (it changes things you see!).
Most commonly, what you will need to do is 'shock' it with chlorine. This can be bought in liquid form and is straightforward to use.
You can also buy an algicide. I would suggest you take a strip test of the pool water and then let us know what it is saying, we can advise further.
When you do add the products I would strongly recommend you leave the pool pump running constantly. A pool should complete a filtration cycle in 12 hours. When you have issues, it is best to keep the pump running to maximise the distribution of the chemicals you are using to solve the issue
It also sounds from your post that you do not have anyone attending to your pool weekly in summer and less so in the winter months. This would have been avoided if you did have someone take care of your pool maintenance... that comment probably sounds like it is not helping, but I do recommend you have someone look after it if you are not always in Spain.
Hope it helps