Algae is typically a result of an imbalance of nutrients and/or lighting.
Allowing any light fixture to remain on for 12 hours per day could lead to algae. Having a light on for a couple hours per day could lead to algae. Finding the proper balance of light levels, nutrient levels and photoperiod isn't difficult but it requires some effort and not just a blanket, one-size-fits-all approach.
Intentional or not, this is bad advice and general misinformation - something we try to avoid in this hobby. Particularly when it comes to sensitive species like shrimp.
Excel is and can be deadly to invertebrates. Excel is Metricide 14, just at a different concentration. The active ingredient is Glutaraldehyde - a common pesticide. Advising a newcomer to the hobby to randomly dose their tank with it is a disaster waiting to happen.
Ammonia spikes - even local/area-specific spikes in a tank - can be deadly to tank inhabitants shrimp. But a tiny ammonia spike isn't always (or even usually) the cause of algal growth.
Buying livestock to try to correct a problem you can't accurately pinpoint can also lead to myriad issues in an aquarium.
It's important not to be argumentative or insulting to other members. Common sense but also a key portion of our Acceptable Use Policy. Intentional misinformation is most unwelcome. Let's avoid that completely.
Algae become visible shortly after an ammonia spike. I put 12-hours of light on my nano tanks to see if lights cause algae. It doesn't. After algae become visible your lights help it grow.
Have you tried Excel? Here's what I do. I do a 50% water change, use one cap per 15 gallons. Turn lights off. Test for ammonia within 8-hours and if you see another spike, do another 30% water change and add more Excel (one cap per 30 gallons). After the algae begins to die (or sooner) buy a few Amano shrimp. They'll eat the dying/dead algae. As the algae change color and die it'll stop eating ammonia/nitrite/nitrate and give you another ammonia spike which causes the problem to reoccur and get worse. That's most likely is what you're seeing.
You may not see an ammonia spike if you have a heavily planted tank - the plants may use it before you do the test.