Actually, it was quite small - as a thumb. Here its photo in 5 g tank:
I had it for 4-5 months, until toxic tank crash and all Echinoderms (including stars) didn't make it, while Crustaceans were not affected at all. Strange.
But I have for 9 months another filter feeding cucumber, more sensitive and big - 6" without tentacles - sea apple, with the same care.
Filter feeding cucumbers are usually sitting in the same position at the top facing flow (<= 100 gph), prefer dissipated water stream (like power filters and Rio Nano skimmer provide) or more concentrated jet from powerhead if it barely brushes extended tentacles sideways. Only 1 of 3 FFC (one pink and two sea apples) was an exception, the exception is still facing the down flow.
Try do not expose cucumber to the air regularly, during water changes. I can't say, how risky it will be - didn't try, but if you search Wetwebmedia site for Pentacta name, it will show post of one guy, who did that and had decline, connected or not.
It is possible to remove sea cucumber from its place, carefully disconnecting its feet by fingers, but it will return at the same place.
In support of my observation of being safe, in case of not mechanically damaging death:
link .
R. Toonen has 3 articles on different types of sea cucumbers, including filter feeders:
Sea cucumbers - Part I: The Medusa Worms,
Part II,
Part III: Sea Apples. I couldn't possibly know, that you already know, so bear with me: when you will feed phytoplankton, especially live phytoplankton, feed not only nannochloropsis, but larger and different kinds, including diatoms. Bottled RotiFeast, Shellfish diet, ESV spray dried phytoplankton contain different sizes and species. PhytoPlan is different, larger.
My sea apple gave bad reaction (closed for a month) on DT Premium Reef Blend (live), but it may work for you.
And: another similar species, as I said, is
Colochirus crassus. Can't say the difference (but if you find it, post it), but I have seen 2 different kinds of pink-green sea cucumber: fine with more intense colors:
and paler large, meaty and generally crude in appearance. Could be different age, could be different species.
I kept mine (and keeping now sea apple) at SG 1.026, temperarure 76F - up to 82F in the middle of the summer, alkalinity on lower side (7.5-8.5 dKH), nitrates preferably below 10 ppm, phosphates below 0.25.
Watch first days, if other tank inhabitants bother it (chromis, percula, mandarin and scooter were safe).
I'm feeding variety of smallest foods available, including phytoplankton and live food, several times a day, aminoacids and vitamins. Including smallest particles from washing mysis, Marine Cuisine, blended seafood, crushed flakes (Formula Two). SS rotifers, frozen L rotifers may be - may be not - be too large. You will see if the water will be cleared from them. Tried Marine Snow and Reef Bugs, but stopped, when finished bottle. One reefer kept sea apple - 6-7" in size - for an year and counting, on Kent MicroVert, tablespoon twice a day, for 40g tank, with less rotifers and ChromaPlex phytoplankton (
link). You also may try some dosing organic carbon, I did that, but not on regular basis.
For you should work whatever food is available, but in variety.
Feeding all tank, but there was described method of target feeding for FF cucumbers
link.
HTH
