You can test this hypothesis out yourself by putting a clump of chaetomorpha into say a 10 gallon tank, get the proper refugium light, get it to tumble and maintain the big 3 (alk, cal, mag). You will see that after about a month, it will stop growing, despite having your big 3 parameters in check as well as salinity / pH / temp etc.
Then after you notice a halt in growth, simply dose a supplement of traces say, chaetogro from brightwell and you will magically see the chaetomorpha explode in growth again. I witnessed this first hand so I can no longer deny the importance of trace elements.