Take the algaecide back! Most algaecides cause foamy water problems and you don't want that. Plus, as long as you keep chlorine in the pool, you shouldn't have an algae problem. I never use algaecide in my pool.
You can't detect a CYA reading below 30 and since yours is a new pool and has only used one puck, you just don't have enough CYA to measure yet. I'm thinking that those pucks are probably ok since they are 99% Trichlor but let's let Ben make the final call on that one. If you do use them, you certainly won't be able to use 8 lbs. of them. They add CYA and you'll need to monitor your CYA level and quit using them when you get to about 50ppm. Then you can just switch to adding a little bleach. But, wait and see what Ben thinks about them. He is right that dichlor would probably be a good choice for your pool instead of the pucks since they also add CYA as well as chlorine, but since you have opened the pucks and won't be able to return them, it would be great if you could use them. What you don't use can be stored until next year as long as they are kept dry.
Your pH is ok at 7.2 but if it goes any lower, you'll want to add a little Borax. With such a small volume, you'll want small doses. I guess I'd try maybe an eighth of a cup and see what that does for you. By the way, those pucks are very acidic and will drive your pH down.
Alk is fine at 130 or 140 with your pool. No more baking soda.
For now, keep the chlorine between 1-3ppm. As your CYA level rises, you'll need to keep it a little higher. See the Best Guess Chlorine Chart in my signature below for more about that.
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