Ray I would just immagine more algea would grow and there would be a chance for increased bacteria and fungus. I am a nurse and not an engeneer so I think more along the lines of bacteria grownth and how much they might increase in a warmed enviornment over a period of time. Actually that is even more a Carolyn answer.
Your tainers are in a different enviornment with the water in the bottom. I am just looking at it from a water standpoint. I do remember that you stated you were going to pump out some of the water part way though so that would be a help to reduce any extra algea growth. I remember you posting pics and having a concern about algea in one of your posts. This
might make it worse. You also posted that you were removing chlorine from your water which I would think Chlorine would actually inhibit the algea growth. But it is a very inventive way to keep plants warm and I wish I had thought of it as much as I have messed with aquariums
Once had a brand new heater short out when I was starting up a brand new salt water tank. Lets just say shorted heater+salt water=fried fish and almost fried Kat
If none of this makes sense or I am just stupid ignore the comment and keep going
Kat