late fees on days for colorado

This is what my lease states for late fees....if any rental installment or other payment is recd later than 3 days after the dare when due,  the parties agree that additional rent amount of $50 or blank percent of outstanding sums, shall also be due and payable. The foregoing items shall b deemed additional rent......it is what is stated on my lease. However, the tentants have been over 2 months behind at times...they owe lattes fee and they agreed to pay late fee in the amount for daily charge of $50 each day they are late.....with my lease stating what I typed...legally as I understand it it jus a one time fee of $50 and not daily late charges...am I correct...I jus want to clear this up before I send out my end of year statement indicated days rent was rec'd in full amount...i would to know what I should do...we had a verbally agreement so what should and how should no charge them correctly. They have breached the contract more than none and I hav not evicted them....