Whats wrong with my Clams?

[MarkoD]

I dose kalk through top off and the separately dose calcium, alk, and mag when necessary

[fishytime]

those aren't the only elements and trace minerals that our critters use .....stuff like strontium, potassium, iodine and a host of others will slowly get used up.....if your not adding these things and not doing regular water changes, then these minerals and elements will never be replenished....

[MarkoD]

So how big of a water change do I need to make an impact. I've got 250 gallons total.

[MarkoD]

actually i just remembered. i did a 10 gallon water change about a week and half ago. few days after i noticed the clams close up. it didnt change anything.

also, this wouldnt really explain why they would open slightly more at night

[sphelps]

So you wait 6 months, then do a water change, then all of a sudden clams start acting up. Stability sounds like an issue unless there's something else you've forgotten about?

[MarkoD]

Originally Posted by sphelps

So you wait 6 months, then do a water change, then all of a sudden clams start acting up. Stability sounds like an issue unless there's something else you've forgotten about?

no. i wait 6 months, clams start acting up. i do a 10 gallon water change. no change except at night (which was happening before and after the minor waterchange)

[eli@fijireefrock.com]

From reading all the posts in this thread and seeing that everything seems in check (but still think you need to make a bigger and more often water changes as you said 10glns for a 240glns tank meaning 0.05% total volume)
In my opinion and past experience I think some or one of your fish has acquired a taste for your clams as you mentioned that they seem to open up at night when fish are not around (as some folks already mentioned)

[sphelps]

Originally Posted by MarkoD

no. i wait 6 months, clams start acting up. i do a 10 gallon water change. no change except at night (which was happening before and after the minor waterchange)

Your previous posts suggested the change was done prior to the clams acting up, hence my previous assumption. Keep in mind a 10% change after 6 months won't have much effect, you can't rule out this issue from that. You can search day and night for some mysterious predator but clams don't have the ability to reason, it's not closing up all day because it's more likely to be attacked then. Clams sense light and touch, they close up temporarily with sudden changes in those senses. The clams are stressed making them more sensitive to light is all.

My honest guess is months of neglect among other things. It was probably a combination of things from the tank being fairly new to a dramatic light change and then the constant downfall of water chemistry from lack of maintenance. In the end the clams have finally had enough and are showing signs of stress which may or may not be reversible. Your best shot is to eliminate the more potential issues with IMO doesn't include moving them or building cages. First check for pyramid snails, these are really the only predator that could cause such issues, if you have them they are easily spotted on the clams foot. Daily water changes of around 20% for the next week or so should slowly bring up strontium, iodine and anything else they require. Calcium and Alkalinity should be careful monitored and even verified to be certain readings are accurate. The water movement around the clams should be moderate and indirect in enhance their ability to feed. Cutting your light back might also aid in recovery as well removing any aggressive type of chemical filtration. Finally I would try intermittent skimming and dosing a small amount of phytoplankton.