Are you referring to polycarbonate panels?

IF SO; then steam. If you don't allow the nozzle to touch the polycarb, it will dissolve the mineral deposits without damaging the polycarb with no chemicals at all, and any drip from the steam is distilled, so it won't leave more deposits.

Once it's clean, if you polish the polycarb with Brillianeze, it will delay another buildup. Not forever, but it will make wiping it all down periodically a lot easier. I proved that for myself on shower doors.

However, if you have the kind of poly that comes in rolls: no clue.

it's the soft poly on a double-glazed inflated hoop house.
we have scrubbed it with a brush in the past, but only with partial success.

Scott

Scott:

I honestly don't know if you could use much heat or mineral dissolving chemicals on that type of poly, but if you have any scraps on hand, experiment with steam heat and both a solution sold for removing mineral deposits, and the old household standby, white vinegar.

To test it's ability to take steam that in fact, is much hotter than anything that comes out of a home steam cleaner, just hold a scrap of the poly material about an inch from the spout of a boiling tea kettle for a minute.

If it passes both the heat and mineral removal and/or vinegar test, then any one, or a combination of them might be a solution for you, and beat trying to scrub soft material without tearing it.

If it will take the heat, I still believe steam alone is the best, because as I wrote before- it requires no chemicals and leaves no new mineral residue at all.

I seriously doubt that your poly can stand the steam.
As suggested you can try it over a tea kettle but most plastic will not withstand much heat.
I would try white vinegar and water solution.

Gardener: I expect you are right, but then: What is it in the rigid polycarbonate to give it such heat resistance?

I steam tested a piece of scrap polycarb and it was not harmed, but I also vaccum seal foods and boil them IN the plastic bags, which aren't much heavier than freezer zip bags, and are emmersed in boiling water for as long as 15 minutes, and have never melted.

The sealer gets very hot, but it's DRY heat and is both compressed into a narrow channel, and applied with some bit of pressure.

So is it the water? I am now quite confused. NATHAN!

Their are a lot of different kinds of plastics.
Perhaps the film on a hoop house can withstand steam but until I have seen it done I would be very careful.
Steam is very hot if it was less than 212F it would be hot water not steam.

Gardener: True about the temp of steam, so obviously polycarbonate is not the same material. But any avenue to solving to solve a problem is worth investigating, so if Scott does steam test his GH poly, I'd be interested in learning his results.

You will need to get a mineral dissolver, its a mild acid. You are suppose to let the iten soak in the liquid, so that want help, you might could wipe it on and it might come off. Personally, I would leave it alone.

Maybe it is becuase of the hard water?

Here is a link that might be useful: hard water solution

I wouldn`t risk using steam on the poly it wouldn`t cope too well.
The root cause is certainly your hard water, if you can switch to using rainwater via a pump instead of the mains supply you would be much better off.
Your poly will last longer too as mains water supplies normally contain chlorine which degrades the uv stabiliser which reduces the life of the poly considerably.
The two main chemicals to avoid with poly are chlorine and sulphur.
A weak acid might be ok but do a test somewhere where it won`t hurt anything before trying a full assault on the limescale deposits.

Use vinegar....