Blue mushrooms languishing

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I bought two blue mushrooms from OA maybe 7 or 8 months ago.

They have not grown in size or multiplied at all.

At first I assumed this was due to low levels of nutrients in the tank ie. low nitrates due to efficient protein skimming and refugium.

However other mushrooms in the tank have now multiplied, only the blue mushrooms are languishing. I have tried them in higher light, medium light, and lower light areas of the tank and still no growth.

Tank specs are all within normal limits and all of the other corals (softies, LPS, zoanthids, shrooms) are doing fine.

Any ideas? It is very frustrating because the blue mushrooms are supposed to be a highlight of the tank.