GHL - adding extra level sensor redundancy for ATO/AWC operation

george7523 · Apr 29, 2025

hi,

i have 2 optical level sensor setup in my sump for ATO/AWC. The auto water change involves first draining out water until bottom sensor is reached then refilling with fresh saltwater back up to the top sensor. When bottom sensor fails to recognize dry state, tank water would be drained pass the bottom sensor and return pump would run dry. Luckily I used a autoaqua smart ac outlet to shut off the drain pump before this happens. I suspect due to the bottom optical sensor being submerged in saltwater all the time, it's more prone to fail. I've had to replaced the bottom optical sensor about 3 times already, each lasting about 1 year.

question:

1. would float sensor be more reliable to use as the bottom sensor ?

2. Without using third party device like autoaqua smart ac outlet, how can I use extra optical/float sensors for redundancy in GHL so that when the bottom sensor fails to recognize dry state another sensor can prevent the drain pump from draining the sump dry ?

Vinny@GHLUSA · Apr 29, 2025

Thanks for sharing the details of your setup. I’ll break down both your questions and offer some suggestions:

Regarding the optical sensor's reliability:
The optical sensor itself isn’t necessarily more prone to failure just because it stays submerged. Its longevity really depends on a few environmental factors and how regularly it's maintained. For example, if it's located near a light source or in a part of the sump with heavy flow or nutrient buildup, you might see filamentous algae or other growth forming on the optical eye. This buildup can block the sensor and cause it to fail to detect the dry state.

In such cases, a float sensor can indeed be a more reliable alternative, as long as it’s also cleaned regularly. Crust or buildup between the float and shaft can cause mechanical binding, so periodic maintenance is key no matter which type of sensor you choose.

Regarding adding redundancy:
In addition to using features like "Maximum on-time" (if enabled), you can introduce a third layer of safety by installing an additional sensor just below your existing lower AWC sensor. Here's how:

Assign that third sensor to the "Leakage Detection" function in the ProfiLux.
Set that sensor to "Inverted"
Go to the Programmable Logicpage, choose an unused gate, then set it to the following:
1. Input 1: Drain Water
2. Input 2: Fill water (Choose the control circuit number where you setup the leak detection function)
3. Function: AND
Assign this PL gate to the Switch Channel that controls your drain pump.

This setup ensures that even if your main lower sensor fails to detect the dry state, the backup sensor will kick in and stop the pump, helping you avoid a dry-run situation.

Let me know if you’d like help setting up the PL logic or have any other questions. Happy reefing!