Table 1. Survey for automatic hydroponic nutrient estimator.

Reference	Objective	Pros	Cons
Khaoula et al. (2021)	ML-based nutrient supply optimization	Vernier sensors are connected to a Raspberry Pi to measure nutrients.	There needs to be more information available regarding data storage or transmission.
Gao, He & Yue (2018)	To regulate and keep track of environmental and water quality factors	A solar-based power source powers node.	The sensor node’s Wi-Fi implementation increases power consumption and necessitates more Internet infrastructure.
Arvind et al. (2020)	Hydroponics system automation using hydroponics and machine learning (ML) edge computing technique	Implemented cloud server to display sensor data	It is only used on a small scale.
Valiente et al. (2018)	Systems for remote monitoring that use TDS sensors	TDS sensors are subjected to calibration.	The IoT-based system is missing a cloud server.