Ok first things first. You should have some chlorine if the SWG is working. As noted above, take a sample directly from the return with the SWG running.
Next, normally we would check for algae using an OCLT.
OCLT Directions This is not needed as you said you have algae growing on the steps. You will fail this test then, but run it if you wish.
So now we come to the most important part. TAKE YOUR POOL BACK! In the process learn the methods here, and never go back to the pool store again! Think of all the money you will save!
First you need to spend some though. This is the most important step, and many are reluctant to do so. You will never succeed at these methods without a proper test kit. Especially when we start to SLAM, this is absolutely needed.
Here are the
Recommended Test Kits. I highly recommend the TF-100 with the XL option. The XL option will give you 2x the amount of the reagents you will go through a lot of during your SLAM. The XL will also bump your total past free shipping.
Next, prepare for the SLAM. Read this, and once you get your kit, do not waver from it.
SLAM Directions The reason you need this kit so much is first you need accurate CYA numbers. The pool store may give you highly inaccurate results if you have them test it. Next, you need to be able to test your FC accurately at higher numbers than your test kit is capable of. Only a DPD-FAS Chlorine test is capable of this.
While you wait for your kit to come in, go to
Pool School.! Read these articles over and over until you understand them well.
Edit: Didn't notice you were in Canada. Still you really need to get the kit.