OK. 150 lb. is better than 100 lb. I'll let Ben decide if he thinks you need a valve in there or not. I'll ask him to look at your thread later.

You're gonna love having a pool! Congrats!

Test your fill water this evening and post the results. Also, go to Walmart and get several jugs of plain, unscented bleach and a couple boxes of 20 Mule Team Borax (laundry aisle). If you want to just add CYA separately, see if they have any while you are there. It may be labeled as conditioner or stabilizer. Check the label ingredients. If it says cyanuric or isocyanuric acid that's the right stuff. Just make sure it doesn't also have a bunch of other junk in it. You'll need about 3 lbs.

OR:

if you prefer to just use a stabilized form of chlorine for awhile which will add CYA and chlorine at the same time, you can use some dichlor. If you have have access to a Sams Club, buy their 24lb pack of 1# bags of 100% dichlor shock. Each bag will add about 7 ppm of chlorine, and about 6 ppm of stabilizer, per 10K gallons of water. Otherwise, order dichlor from Amazon:
Kem-Tek Dichlor 22 lbs
We do NOT recommend buying dichlor locally, otherwise, at least until you are an EXPERT reader of chemical labels. The chlorinating pool chemicals sold at Walmart, Kmart, Costco, and most other local stores are diluted blends, sometimes with copper and other products with bad side-effects. (You won't need all the bags of it because your CYA will get too high if you use all of it, but you can save the ones you don't use for next year.