The two should be ok together.
I have a hob fug filled with razor, bubble and fern caleupra
Are you keeping it pruned back sufficiently to prevent it from going sexual and disintigrating?
Cheato I beleive is NOT
Halimeda which will require relatively high Ca
levels to thrive.
quote "They need calcium ions and fairly high alkalinity to grow AND the nitrates and phosphates levels must be kept very low." from http://www.globaldialog.com/~jrice/a...e/halimeda.htm
edited to remove any association between chaeto and halimeda. they are not the same. they should never be confused as being the same. they are different.