What Ant said. The battery has been called out multiple times. The voltage is only whats required to drive the current through the elements in the network. Your LEDs nominally use ~20mA but thats variable within tolerances PLUS the resistors themselves are using current to change the voltage (watts). This is the inherent inefficiency of parallel arrays and the reason you have been getting a hard time about your parallel setup. EVERYTHING is pointing to insufficient power supply. By that we mean: not enough Amps.
Im also into saltwater tanks and over in that community everyone is trying to get as many LEDs in series on a driver as they can for their lighting. Power consumption is a big deal because it adds up to big electric bills. In addition they want consistent current going through as many LEDs as possible so all of the emitters are the same brightness. In most applications series LEDs is by far the preferred method of powering LEDs. Over here making models you need to make compromises because sometimes you can't get as many cells into a space as you would like or don't want to risk a LED dying inside your model where you can't get to it and fix it.