Two points you should be aware of.

1) Anti-freeze contains glycols (ethylene or propylene). Ethylene
glycol is cheaper, but it is toxic. In the US there are plumbing codes
that specify the use of proylene glycol where there is any risk of the
anti-freeze contaminating the domestic water supply, i.e., an indirect
DHWS cylinder.

2) The hot glycols in the anti-freeze will combine with any dissolved
oxygen and will form acidic compounds; I can't recall the formulae.
The solution will start off with a pH of 10 or 11 (alkaline). Once it
becomes acidic (pH 7), it becomes very corrosive, causing rapid
galvanic corrosion. You need to monitor the pH and change the
solution, or replenish the corrosion inhibitors to maintain the pH.