On my '88 Accord, I was given some free "water pump lubricant" from someone who worked for Casite. Of course, back then, we didn't know any better. I get a call from my then-wife saying the interior of the car had filled up with steam--the heater core had sprung a leak. I tore that thing down to the firewall and replaced it. Just as I'm filling up the radiator, that sprung a leak!! So whatever was in that Casite stuff rotted away both the heater core and the radiator.
Use only the Honda coolant, right from the dealer, and that's all you'll ever need. Additives don't help anyone but the investors of the companies that make them.