There are three ways that a sea apple commonly dies
1) starvation
2) unstable parameters
3) stress from other tank mates
To prevent 1) even phyto and/or copepods daily. Sea apples natural behavior in the ocean is to open at night. Since it's in a tank and there aren't enough "food" for it it gets confused and will try to feed (opening up) at random times a day. Technically this is bad but as long as you are able to direct feed it phyto or copepods everyday this shouldn't be a problem. Don't worry if you accidentally miss a day feeding just don't miss it often.
To prevent 2) keep everything stable aha
To prevent 3) watch out for anything picking on it. Even non aggressive fish will pick at it's feeding branches thinking it's food causing it to close up and never get to eat which will lead to you saying goodbye to everything including your wallet.
I'm kidding
Usually sea apples don't nuke your tank with toxins if nothing bothers it. If it dies from starvation it'll just die.
Like anything else if it dies in your tank and you don't take it out it'll cause an ammonia spike.
Summary: feed daily and keep parameters stable
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