Neat idea! Don't think I've seen it done before.
Only one potential issue I can think of. When freezing solutions, sometimes just the water seems to freeze, pushing the dissolved substance out and concentrating it. I forget what it was, but once this produced a block of seemingly pure water with a layer of "goo" on top.
If something like that occurs and the active ingredient sticks to the tray or your fingers and never makes it into the tank, it might change the dosage somewhat. If that occurs with Excel, concentrated glutaraldehyde is also a well-known sensitizer, repeated exposure can lead to contact allergies.
Not sure if any of this will really happen, just speculating.
On the positive side, perhaps one could make single cubes of solutions that can't normally be mixed, by freezing them a layer at a time.
i use one cube exclusively for the the Excel, and one for the other mix, like iron, flourish,Potassium.spreading the 7 day dose out over the week, for those three, only fill one cube about 1/3
"When freezing solutions, sometimes just the water seems to freeze, pushing the dissolved substance out and concentrating it"
i gave that a thought, but than again it's still the same amount in the one cube for that day............right?
and i wash the trays out in hot, hot water before i refill on sunday night.
sorry i see what your saying about active ingredient sticking to the tray.
yes some "residue" is left in the cube after i pop them out but it seems like very little.
i only did iron tests after i started doing this, and the spikes stoped.
i was getting a barely detectable reading from my test kit on the third day after "weekly dose" from a good 0.3 on the first day.
to a solid 0.4 every day the next week after starting this