Ed. Code, § 15738

The Controller shall make the deduction provided by Section 15735 during each fiscal year, as herein provided, until the principal amount of the apportionment made to the district for the grade level, and all accrued interest due thereon, has been withheld; but no interest shall accrue or become due and payable to the state with respect to the principal amount of any apportionment after the expiration of 25 years from the first day of July of the fiscal year next succeeding the date of the warrant issued by the Controller covering the payment to the county treasurer of each portion of the apportionment. At the expiration of 30 years from the first day of July of the fiscal year next succeeding the date of the warrant issued by the Controller covering the payment to the county treasurer of each portion of the apportionment, any unpaid balance of the principal amount of the apportionment, including all interest included in the principal amount, shall be canceled on the books of the Controller, and the state shall have no further right to the repayment of the unpaid balance.