I am installing a new chair carrier and toilet on a very old docks planking floor I have secured the carrier as tight as possible to the floor but when the toilet in installed the carrier flexes about an 1/8 of an inch I have determined that the floor is actually flexing up and down with the carrier I have tried the make legs out of strut for the rod and have also bolted the carrier down through the floor to a piece of strut underneath has anyone ever encountered this or have any ideas for a fix

It is supposed to be bolted the studs in the wall, NOT just to the floor. It would be impossible to anchor it to the floor unless it was poured into concrete.

This is a commercial application so the studs are thin gauge steel

I wouldn't have attempted to install it until someone had come in and reinforced the wall. Is this a conversion to make something ADA compliant?

No it's a zurn commercial carrier so there is no design to attach to studs they bolt to the floor they work just fine on concrete but the docks plank are just not solid enought

can you access the floor from underneath?

What is the part number of this carrier. Even Zurn's carriers for wall outlet floor mounted toilets are secured in the wall. Also they are designed for penal institutions… you aren't building a private prison I hope…

Lol model number is a zurn z1203 nr4

Then they have to be "backed up" with wood studs. Any construction company knows that and how to do it.

Then you either need "stud mount" carriers or a wall support bolted to the top carrier bolts.

Floor supported toilet carriers are designed for concrete floors, NOT wood. There is almost no way to stiffen a floor enough so that it resists the stress of a person sitting on a wall hung toilet.

Plenty of ways if you can access the floor from below.

Docks planning is cement from into sections such as 3'x20'with concrete poured on top of it

How much concrete? A 2" topping will probably not be adequate to stiffen it.