Chondrilla nucula

Acclimation: like all invertebrates it is very sensitive to even minor changes in water chemistry; acclimate it slowly, by floating or drip, without rushing. Above all, NEVER take it out of the water, whether at purchase, in transport or during acclimation: even brief contact with air traps bubbles in its pores that block the flow of water, and the colony then starves or decomposes.

Placement: put it in moderate to strong flow that brings food and carries waste away, but never where air bubbles can be forced into the colony (skimmer outlet, agitated surface). For most sponges light matters little; strong light grows algae on the colony, which clogs its pores and stops it feeding.

Difficulty and risks: Meerwasser-Lexikon rates it of 'average' difficulty and advises at least 100 litres. But above all it is a coloniser: in Bermuda a Chondrilla recorded under this name uses toxins (allelopathy) to overgrow attached organisms, mostly corals, and one study attributes 43 to 51 % of the observed coral overgrowth to it. Wikipedia (it) calls it highly toxic to most other marine organisms. If it arrives on live rock, keep it away from corals and remove spreading sheets.