An optimal control algorithm is derived which minimizes at each time instant the one-stagek-step-ahead performance index for the state-space representation of the CARMA model. Equivalence of the input-output representation in its asymptotic form and in the Clarke-Hastings-James algorithm is proved. Formulae for computing the output and control variances at any time instant for both optimal and asymptotic algorithms are given. The results are illustrated by a numerical example.