Our 2 cents
If you just got the hammer then it could be lighting (too much and too little light will cause them to "melt"), params, initial shock; so the next week will be crucial. We have multiple hammers in house and have seen them freak out when something malfunctions or someone makes a mistake maybe dosing and params are out of whack.
Hammers are very sensitive and will give you signs early they are not happy and something is off in the tank. Typically, when hammers start to not open fully it is either "pests" or params in the tank. They do not like alk swings, 9-10's are usually where you want things to be all week long. If you have not done a water change in months for example, you could be low on some critical trace element. You want to also ensure your nitrates and phosphates are never 0, this allows for water column balance per bacteria/algae to go out of balance thus starts to affect inhabitants. If your not seeing them recede then usually they are just "upset" vs loosing flesh then they are starting to die. Flow, medium is typically where they do best so they don't throw a head.
We have found ideal params for most hammers are:
alk 9-10
calc mid 400's
mag upper 1300's
nitrate and phosphate above 0 (never good to hit zero)
ph 8.1-8.3
Also, less is always more. So any adjustment you make, you should wait a couple days and see how it goes as they do not like change. Typically for example, if our alk gets out of whack for some reason it takes 7-10 days for them to return to normal after we get levels where they need to be. Just calling out, dont make 10 changes on day one and then have no idea which one really helped or worse 1 helped and 9 made it worse!
Good luck, always nerve wracking...