Saltcorner
By Bob Goemans
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Bob Goemans corresponds with Jim McKinley

Jim McKinley writes...

Hi Bob,

Although my alga problem is now 85% under control, my corals are still not doing well. A new saltwater aquarium store with beautiful corals just opened near me, and I am excited about making major modifications to my system (which I will tell you about in another letter). But for now, I'm wondering if you would mind sharing answers to a few questions:

1) Regarding the flow rate from tank to sump, how many water 'changes' per hour do you recommend?. (My tank is 500 gallons; Moe recommends 3 - 6 changes per hour which would require a pump that moves 1500 -3000 gal/hour....do you agree?). I'm guessing that the exchange rate need not be much greater than the flow through the skimmers, if the skimmers are the only apparatus associated with the sump.

2) I'm purchasing a MTC HA-3000 skimmer and plan to use my current ETS skimmer for ozone.

a) With such a setup, which skimmer would you have first in series: ozone first, then "non-ozone" skimmer, or the reverse order. If it doesn't make much difference, I may just buy one pump (Sequence 3500 gal/hr) to operate both, in which case the effluent from each skimmer would be mixed in the same compartment of the sump, negating the possibility of having one follow the other.

b) Given a choice, would you prefer a skimmer or an ozone reactor to add ozone? (As mentioned, I have an ETS already, but would consider purchasing a reactor if you think the reactor is superior.

c) Are you confident that ozone, used at the rate you recommend, is safe? (Sprung cautions about the possibility of ozone producing bromide toxins.)

As always, I value and appreciate your advice.

Thank you!

Hope all is well.

Jim McKinley

Bob replies...

Hi Jim,

Thanks for the feedback, and the unwanted red algae, Asparagopsis taxiformis, has been a demanding and an exhausting battle to resolve, as discussed in your past letters! But I'm happy it's coming to a close.

As for your questions;

1) Water flow through the aquarium itself, i.e., around and over the coral animals, needs to be similar to what is experienced by them in nature. The sea is not a stagnate area and flow to and over the coral animal removes their waste products and brings important food and elements essential for their well being.

The stagnate water layer over the coral animal is called the "boundary layer" and its thickness is dependent upon the velocity of the water impacting the animal. The thinner the boundary layers the better the metabolic gas exchange. That relates to better carbon dioxide and oxygen exchange whereas thicker layers relate to slower diffusion rates that impede important calcification processes.

Even the delivery of valuable foodstuffs is impacted by water flow. If too slow, zooplankton may be able to maneuver its way around the coral animal. If too fast, the coral animal may not be able to capture the amount of zooplankton or phytoplankton needed to sustain itself.

How to describe the intensity of that flow is difficult to explain and words such as good or strong leave a lot to be desired. There are also varying degrees of water motion in the wild depending upon the season, wind conditions, time of the day and just where on the reef or lagoon the measurement is taken. As for the measurement itself, it is usually taken in inches per second, something the hobbyist would have difficulty in measuring.

To make the subject matter of water motion usable for most hobbyists I've decided to relate to the visible intensity of water motion on that of a long tentacle anemone. No visible tentacle motion is "0" whereas a slight movement of some tentacles is "1." If all the tentacles are gently swaying in the current it is a "2." If they all are moving fairly fast and bouncing into each other it is a "3." Should all the tentacles be driven with such force that they are extended in one direction or unable to sway back to their central position it's a "4."

Mushroom coral would require a #1 or #2. So would Carnation corals (Dendronephthya spp.). Most Acropora would do well in the #3 to #4 ranges. Cup or funnel-shaped corals, e.g., Turbinaria spp., also require the #3 to #4 ranges so as to keep detritus from collecting on their surfaces and their central areas healthy. Keep in mind that excessive water flow can keep the coral animal from properly expanding to capture light or needed foodstuff. It can also cause tissue abrasion or even rip the tissue.

Because pumps, especially powerheads, are susceptible to a slow buildup of calcium carbonate and slime, their efficiency diminishes with time. Keep in mind to setup a schedule to clean powerheads every six months and check flow rates of main system pumps at least yearly. Also keep in mind that many water pumps, and especially powerheads, usually fail to deliver their rated water flows mainly due to the situations surrounding their installation. Always purchase water pumps that will deliver more flow than what would be needed to meet system requirements. High pump flows can always be modified by using valves to reduce flow, but insufficient flows can not be rectified without additional equipment.

And as to 'possible' exchange rates so as to simply judge a main pump size, Dr. Jaubert in previous letters between us recommended 3 - 5 turnover rates, which falls into the Moe recommendation. And to achieve this, the main pump needs to slightly exceed that rate because of head pressure and turns and twists in its plumbing connections. And if you base animal movement on my above recommendations, a too large flow can always be throttled back with a gate/ball valve.

2) Excellent skimmer equipment, and its always better to have the skimmer not using ozone first inline because ozone would oxidize the very nutrients the skimmer is designed to remove, therefore reducing its foam production, if not eliminating most of it! Then somewhat downstream from that one, ozone can be applied to the second skimmer without being concerned about reducing its foaming capability. And as for an ozone reactor, it's a more complicated piece of equipment and suggest you not use it as your second skimmer (which ever one you choose as both are super products) is of excellent quality and should easily handle the level of ozone dispersal discussed in previous letters. And since ozone reacts with chloride and bromide ions in seawater, it results in hypobromus acid. Therefore, some salt mixes limit the use of bromide in their mix so as to reduce this possibility. Bear in mind the effluent from an ozone contact chamber must be passed over a bed of activated carbon to remove residual ozone before it returns the aquarium. Even though residual ozone is fairly short lived, usually less than an hour, the residual can damage fish tissue and invertebrates. Various manufactures make ozone test kits for those who may want to test for a residual in the flow before and after the carbon bed. Yet, a simple swimming pool test kit that tests for free chlorine or DPD 3, is suitable for assuring this possible aspect is within safe operating parameters, i.e., not to exceed 0.05 ppm for fish or 0.02 ppm for invertebrates. Properly controlled/metered amounts of ozone should not normally present any problems to fish and invertebrate.

Hope this helps and keep me posted.

Cheers

Bob

Keywords:

Protein Skimmers; Ozone; Flow Rate

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