I have an 8 gal biocube. All corals are doing well and thriving except one frogspawn. Its polyps are starting to shrink and recede. Another frogspawn (different variety) is just 7 inches away and is thriving, getting huge. Both have the same flow, under same light. Any ideas? It was doing really well until about a month ago. Then one head was shrinking and now the other.