Ice packs to chill tank in summer?

[GoFish]

Update
Added 8 cups worth of ice in a ziploc

Before 81.4 f
After 79.6 f

I'm not really doing this in desperation. Just wanting to reset the temp at the end of the day as the house doesn't get cool enough overnight to bring it back down to the 79 f range where I want it. Everyday during this heat wave the temp climbs higher than the last, because it doesn't cool enough during the evening. So far this is working.

So as of last nights addition.
1.9 litres of ice cooled 170 litres of water by 1.8 degrees.
I'll try to utilize this calculation either tonight or tomorrow and see if I get the same results.