to me it looks soft but really only you can tell :l its not a take a pic and we can see kind of thing its also a feeling physically (like with your hand touch it)
also what kind of tetras?
if neon tetras; neon tetras tend to occupy streams amidst forests -- specifically clear-water settings. The water in their natural environments usually is a tad acidic and often is brownish in coloration because of the presence of decaying organic substances that cause the acidity. However, the water in their habitats isn't always dark; even with tannins it sometimes appears totally clear.
Optimal aquarium temperatures for neon tetras are between 72 and 78 degrees Fahrenheit. Rainwater is perfect for keeping neon tetras in strong working order -- these fish like pH levels between 5.5 and 6.2, though anywhere between 5.5 and 6.8 is appropriate. Hardness of between 2 and 10 degrees dH is recommended. Although soft water is undoubtedly favorable for neon tetras, these fish can manage in medium-hard water if it is of a high grade. While they can handle hardish water for minimal spans of time, extended exposure to hard water could have negative effects on their life spans. For reproductive purposes, neon tetras require pH levels of no more than 6.5, also with extremely minimal hardness.
Neon tetras easily pick up on any shifts in their water, so always make any adjustments in a gradual and measured manner -- you definitely don't want to shock the poor things out of nowhere, after all. This includes water temperature -- make sure the temperature is steady, regardless of where in the appropriate range you keep it.
