Pool store analysis are notoriously inaccurate. And, time at the pool store is time that is either spent trying to NOT buy the chemicals and quick remedies they want to sell you or time that could be better spent.....like swimming. You really need to invest in a good test kit. The TF-100 is a fine choice at tftestkits.net. There are other similar test kits out there. The important part is to ensure the kit has the FAS-DPD chlorine test. That is a must to test for chlorine at the elevated levels required to shock your pool. I know they are kind of expensive, but with the money you will save using the BBB method of pool care, you will more than pay for the cost of a good kit.
I would also strongly recommend spending some time at pool school reading to gain some knowledge. There is a link to pool school at the top, right corner of this web site. The articles there will at least familiarize you with the basics of pool care and the BBB method recommended by most of the TFP subscribers. And, when you are done reading, feel free to ask questions. All of the members here, and especially the moderators, are very helpful and want you to have a sparkling clear, sanitized pool as badly as you do.
To answer your original question at the start of the thread.... You need to shock your pool. Read the article at pool school about shocking, as it is a process and not a product you buy. Once you pass the overnight FC test (as described in the aforementioned article), your pool may still be cloudy due to dead algae that still needs filtered out of the water. On some occasions, continued cloudiness may point to a filtration problem, but in most cases it is merely indicative of the need to shock, brush, and filter 24/7.
In order to shock though, you need a good test kit (sounds like a broken record, doesn't it????) to be able to monitor FC levels.
Hope this helps.