Hopefully others weigh in, but I do not believe it will be harmful to your fish. You may have a high amount of nutrients in the tank, and if you combine that with a long light period could cause algae. Fast growing stem plants to eat up the nutrients would help if algae becomes a problem.
Most likely will lead to water clarity problem's and as mentioned above ,with too much light either in intensity, or duration,,lead to algae bloom.
I believe these tab's to be comprised of largely iron and maybe some trace element's but I am not sure .
Maybe add some fast growing water sprite to the surface or rooted in substrate to help gobble up whatever they are comprised of?
I don't know about seachem root tabs but with the O+ tabs the nitrate will spike if you put too many. My nitrate went up to 160 after i added too many O+ tabs in 36g tank, i think i added about 10-12 tabs ..