Welcome!
It's Friday now. No reason you can't be swimming Sunday. You drink the same water -- it can't be toxic!
First advice: do what Marty suggested. Order a test kit. It's an investment and will save you much grief. One trip not made to the urgent care with pinkeye or an ear infection and it's paid for. One trip to the pool store to get the water tested because it turned green will likely end up costing you more than the test kit, too.
There's a steep learning curve, and a lot of reading in Pool School. You can skip the test kit article and go straight to
TFTestkits.net an dpick up a TF100. I've been using one for years now.
Now, of immediate concern. What to add? When? Those can be answered in
ABCs of Pool Water Chemistry and
Recommended Pool Chemicals - Trouble Free Pool and
PoolMath - Trouble Free Pool
But here's an immediate answer to lower your anxiety a little. Get the pool filled and the pump and filter running and check for leaks. Then pour in about a quart (note the jugs are no longer a full gallon) of 6% bleach. Plain bleach. Look for the strength on the label. No strength, no buy. And avoid scented or splashless or any other improvements. That is getting hard to find in a grocery store, so you might want to check the pool section at a big box store or hardware store for pool chlorine. It'll be stronger so you'll use less. Just post and ask how much when you know what strength you have. Just dribble it into the return stream so it will disperse and mix.
In a perfect world, you would now be checking pH and making adjustments. But you don't have a test kit, so you can't. The good news is, if the water is drinkable, it's not likely to peel the skin off and nobody treats the fill water before they take a bath, right? As soon as you get a test kit, pH needs to be adjusted, because it will change over time and you run the risk of skin irritation and burning eyes.
So now there's some chlorine in the water so let the kids in. It might not be a bad idea if there's a lot of kids to add more bleach again after they get out.
Moving on.... that quart of bleach isn't going to last very long without some sun protection. Let me say this right now: you will need to add that much bleach every single day until you get a test kit. Then you can measure things and dose it accordingly. Sun protection is CYA. Cyanuric Acid. Pool Stabilizer. That's in the pool aisle at those same big box stores. Just read the label. It'll say Cyanuric Acid or Isocyanuric Acid. You want 99-100% strength. Get it home and add 2 lbs (doesn't have to be precise) by pouring it into a hole-less sock or nylon and tying it securely and hanging it off a pole or something so it gets pummeled by the return stream. It'll take a few days to dissolve.
Once you have test kit in hand, test! Then you can post a new thread and find out what needs adjusting. Once you start doing it starts to make sense. It'll feel overwhelming for a couple weeks and then suddenly you'll have the revelation that, "This is pretty easy! Why was I stressing?"
