A word of caution for PPM.
Fertilizer application rates are typically given in terms of lbs/acre. When we describe fertilizers we discuss it in terms of ppm. However, it is important to keep in mind the overall mass of fertilizer in smaller water volumes will be less in shorter/smaller tanks or "long" aspect ratio tanks. Even generally rectangular tanks will have disparities of application rates in the range of 20% (60p vs 90p). Therefore, it may become more difficult to maintain "low nutrient" systems in these smaller tanks because your plants will bottom out on nutrients faster when compared to taller tanks.
Thus to maintain the same rate of growth (mass gain) in smaller tanks while avoiding stunting it is better to err on the side of higher ppm of fertilizer.
Fluval Spec V
7x Microsynodontis sp (1)
1x Cranwelli Horned Frog