| Time Line | PO4 Level | Comments |
| Upon set up of the tank | 0.03 ppm | It is assumed that this was PO4 resulting from precipitated phosphate on the rock in the sump. The fact that is was present did not impact the test, since we are trying to determine the impact of PO4 to begin with |
| End of week 1 | 0.06 ppm | Increase probably as a result of some die-off on the rock in the sump, and as a result of foodstuff decay. No real impact visible on coral at this stage. Coral opens fully and extends tentacles for feeding at night. During the day the meaty large polyp is quite inflated and appears in excellent condition. Polyp overlaps the exoskeleton nicely as it should. Estimated overlap is more than one inch. PO4 in the control tank is measured at a level of 0.02 ppm and the coral looks in excellent shape, fully open and feeding at night. Coral expands and polyp overlaps the exoskeleton. Overlap at least one inch. |
| End of week 3 | 1.1 ppm | Coral in test tank appears to show signs of stress. Coral is not opening as much during the day. Overlap of polyp is smaller and estimated at less than 3/4 inch. Coral not as meaty. Feeding at night normal. Coral in the control tank doing fine and not exhibiting any signs of stress. PO4 level in that tank is 0.03 ppm. Overlap of polyp is larger and coral is "meatier" in appearance. Polyp appears to have become larger. The exoskelton (looking at it from underneath the tank shows signs of growth. The color of the growth areas of the exoskeleton is not as dark as the rest of the exoskeleton. |
| End of week 8 | 1.5 ppm | Coral is definitely stressed. Polyp appears to have shrunk. Edges of polyp not as green. Overlap non existent. Top of skeleton can now be seen easily. It appears that this level of PO4 is already too high for the coral and that the stress actually started at a lower level (see results of End of week 3. At this stage a decision had to be made: do we continue the test and let the PO4 rise even further, or do we lower the PO4 and observe what happens. It was decided to continue the test to determine what would happen if phosphate levels increased. This was not an easy decision as we did realize that, more than likely, we may be condeming the coral. On the other hand, to validate Peter Wilkens' findings we needed to continue. The coral in the control tank showed no signs of stress at all, on the contrary. It was doing very well and showed signs of a small amount of addtional growth. Polyp extremely meaty and expanding way over the edge of the exoskeleton. PO4 in the test tank was at 0.02 ppm. It appeared obvious that the high calcium levels and the supplements used were beneficial to this coral and were inducing growth of both the skeleton and the polyp itself. The test on the control tank where PO4 was real low indicated that this coral was certainly not under stress, on the contrary. |
| End of week 16 | 1.9 ppm | It is interesting to note that the phosphate level did not rise all that much during the period between week 8 and 16. Skimming and natural biochemical processes are probably the cause but we did not investigate this, as this was not part of the experiment. One can assume, and I realize that this is dangerous, that the filtration media in the sump was breaking phosphates down and that elimination from the system was in due to a combination of the skimming and the addition of Kalkwasser. We did note precipitates in the tank and on the rock in the sump. The coral appeared severly stressed. The polyp had shrunk and was no longer covering the entire skeleton. Polyp tissue loss had occured although no necrosis was visible. The left edge of the polyp appeared loose. We used a thin wooden stick to probe and move that portion. This confirmed that the tissue had detached from the skeleton. Overall two negative effects were evident: shrinking of the polyp and detachment starting. We decided to continue the test to evaluate what would happen in the ensuing weeks. |
| End of week 20 | 2.2 ppm | The coral was no longer what we would consider saveable. Its polyp was by now close to half the size of what it was when the experiment started. The left side of the polyp was not only loose but showing signs of tissue breakdown. This was confirmed by touching it with a wooden stick and observing pieces coming loose. This could actually have been infered from the amount of material the skimmer was removing, and the deep yellow color of it. It was apparent that the experiment confirmed Peter Wilken's findings for this coral (again we cannot generalize, but this scenario is certainly food for thought for those who have run into tissue loss, shrinking of polyp tissue and detachement of portions of a polyp from its skeleton in other species of corals). Because of the sad condition that the coral was in the experiment was terminated. The coral in the control tank was doing very well and had expanded its skeleton by about 3/4 inch. This is somewhat lower than what Wilkens suggests as possible growth when this coral is kept under excellent conditions. |
The overall conclusion was that Lobophyllia was very sensitive to PO4 levels. Although we did not do a reverse test by lowering the PO4 levels to determine what would happen if we decreased them, it appears that levels of around 1 ppm are too high for this coral (see comments on the coral at the end of week 3 of the testing.
It would have been even better, from the standpoint of confirming this nefarious impact of PO4 on Lobophyllia, if I had been able to conduct this experiment several times.
The fact though that the matter was brought up by Wilkens, and the fact that the control tank in which phosphates were kept well below 1 ppm with the coral growing and showing a meatier polyp, appear to indicate that if this experiment was duplicated that one would obtain the same result. Only additional testing would further validate my findings. I am aware of this.
I cannot definitively state, therefore, that the test was fully conclusive but the indication is that the likelihood of it being indeed so, based on the findings, is very high.
Anyone willing to invest the time and money to conduct a similar experiment is encouraged to so and share their findings with me and others. Indeed, if PO4 has an impact on corals and if we have not taken this into account in how we maintain water quality levels then this fact is certainly one that should be brought to the attention of as many hobbyists as possible. This is even more so if the impact of PO4 can be demonstrated on other species of corals as well.
As such, this test is just a beginning of perhaps a new dimension of water quality that we need to be aware of and take into account when recommendations are made.
Of course, I have been recommending real low PO4 levels for a long time but mainly to prevent the appearance of micro-algae, not with the specific intent of coral health.
I would appreciate if the results of this testing could be disseminated, so others may hopefully follow up on it and conduct additional testing. If all of you who read this, cross post to other lists and indicate where this document is located, maybe others will share their own findings, or will set out to perform similar testing on the same or other corals.
The benefit of it is that we can learn yet more about the importance of the water chemistry in our tanks and how it may affect the health of our corals.
Albert J. Thiel, July 1997, Tests conducted in Las Cruces NM between July and December 1996 for a total of 20 weeks.
Footnote
The coral in the test tank had to be destroyed. The coral in the control tank was sold to Julio Lopez of El Paso, Texas.
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