Consider an elevated platform in relatively deep water where platform is supported to be about 2' underwater and covered with about 2" of pea gravel or sand. Just about any substrate will work. Border platform with a 2" to 4" rim to prevent tail-sweeping males from displacing substrate from the platform. The arrangement will not increase nest numbers but will make so they are likely more easy to monitor.
I use such in larger tanks (~2,000 gallons) where individual nest bowls formed by rubber bowls or 5-gallon bucket bottoms are supported by 8" x 8" x 16" concrete blocks standing on end. Blocks will not work on a soft bottom.
