I use Excel.
There are 3785.41 ml in ine US gallong. I add 3 ml of Excel per 10 gals of water. That means 3 ml in 37,854.10 or 1 ml/12,621 (I had to add the 3 ml of excel to the total). If the Excel were 100% glutaraldehyde that would be one thing. But I highly doubt that is the strength of Excel.
There are 3785.41 ml in ine US gallong. I add 3 ml of Excel per 10 gals of water. That means 3 ml in 37,854.10 or 1 ml/12,621 (I had to add the 3 ml of excel to the total). If the Excel were 100% glutaraldehyde that would be one thing. But I highly doubt that is the strength of Excel
What is a glutaraldehyde used for?
Glutaraldehyde is a colorless glass-like crystal that is usually in a 2% to 50% water solution. It is used for cold sterilization of dental and medical equipment and as a preservative, biocide, hardener, and tanning agent
Glutaraldehyde - Hazardous Substance Fact Sheet - NJ.gov
My bet is that the stength of what is in Excel is pretty diluted. It is also likley somewhat modified from pure Glut. but this is a guess and who knows if that makes it less potentially dangerous. But we we are talking about here is a pretty low concentration.
Next, we have a lot of anecdotal evidence in the form of this product being used for a few decades in what is likely a fair number of tanks. I have been using in most of my planted tanks after weekly water changes now for about 20 years. My fish appear healthy, they mostly live longer than average life expectancies and I rarely get diseases etc. I keeps and breed some rare exepensive fish which are quite prolific and not deforemed. Poeple who get them have them spawn as well.
I do not overdose Excel ever. I do not use it as an algaecide. Fertilizers of all kinds are diluted before going into a tank and then gadually with refilling. Finally, from the time I add the Excel it is being used up by the plants. so the ceoncentration is decling steadily between applications.
What I cannot say os that here is nothing living which we might keep in a tank that will not have a problem with Excel. I have not kept anywhere near close to that many different fish to say this.
I do not begrudge anybody for not wanting to use Excel or a similar product, that is their decision. But I also feel there are two sides to this and my experience comes down on the side of safe to use properly. I should also mention that I have also done a pressurized co2 tank and never used Excel there.