Sorry. But its difficult to follow you. Let's try to work together to get to the bottom of your problem, your plan, and how we can help.
Hi, I have absolutely ZERO chemistry knowledge and experience.
Um. OK.
Where I live we use extensively underground water
That's a oddly constructed statement. Maybe you want to say, "We have a well for household water."
which is very hard and full of lime.
A common problem worldwide. There should be a number of commercial solutions available.
All the windows in my home have this white film on them.
That seems like a non sequitur. Don't wash your windows with tap water, or something.
I am wanting to make a lime filter and have done some research.
OK. You could just buy a commercial one, but good work with the research. Let's see what we can use.
I believe a siliphos crystal filter can be put in line.
I can't find good information on that. It seems like a commercial product, but the specifics are lacking or dubious.
I could not find Siliphos crystals but was told that SHMP (sodium hex ametaphoshate) is the same thing.
I'm not seeing that they are the same thing. But I'm not studying Google that rigorously.
When looking for it in a crystal or granular form all I found was it in a powder form, this wont work as an in line filter. Is there any way to convert the powder to a crystal?
It may be possible. This is something we may work with together. It may not work at all however, so we may not bother.
I then found a recommendation to use citric Acid,
A good lime remover yes. Commercially available, in cleansers, at a reasonable price. Also purchasable as a food additive (I put it in my Borsht and drinks) but at a premium price.
If I was to combine citric acid and SHMP would this make an effective lime scale removal solution.
The citric acid in water would help definitely. I like to drink a quickie lemonade made this way. You do realize that acid in water tastes like sour, right? You can't de-lime your household water this way, unless you want to shower, cook, wash your clothes and hands in lemonade.
Would it help reduce the time tell the lime scale builds up.
It would really be simpler to purchase a commercial lime remover.