I'm working on a project involving Pure Data and Arduino. The idea is to play an audio file while controlling a pump that breathes air into an aquarium, based on the envelope of the audio, so that the bubbles correspond to the voice that you hear in headphones.
My problem is, while it works perfectly with one aquarium (playing the audio file + controlling the pump), it's less precise, and sometimes completely off, when I'm adding the others.

Files : main.pd, aquarium.pd, arduino.pd

The logic of one aquarium is inside an abstraction, [aquarium], with the file, threshold, audio output and Arduino pin as creation arguments. Every instance of the abstraction is playing its own file into a given audio output, and sending messages to the Arduino ("turn on pump X" or "turn off pump X"). It works quite well for most of the aquariums, so I guess (hope) the fix must be simple.
I tried different ideas to limit the message flow but didn't quite succeed (hence the mess below the [dac~] object, this stuff is not used anymore).

I only recently thought about increasing block size, thinking that would reduce the number of messages sent to the Arduino. However using the audio settings, it didn't seem to change anything, and I'm not sure how to use the [block~] object. Do I have to send the audio output through an [outlet~] object? I guess that would mean each of my 9 [aquarium…] blocks would need to have 9 outlets going into a [dac~] object in my main patch, and that would be a big spaghetti plate :)

I'd be curious to know if any of you has ever encountered this kind of issue, or has an idea to fix it, either with block size, pure data magic or anything else…