Some observations

[Ruu]

Just thought I'd throw in my 2c. I have a 2 x 65W PC fixture (10k / actinic) over a 24" deep tank. Many people seem to think that this is all wrong for macro growth, yet I have explosive growth (doubling every week or two) of caulerpa racemosa, solid growth of razor caulerpa, erratic growth of an as yet unidentified grape-type caulerpa (swings between explosive and near death in a two week period) and some slow growth of chaeto (although I might attribute this slow growth more to the nutrient export properties of the racemosa than the lighting).

One comment I might make is that I didn't see great growth until I dialed my skimmer back (went away for a week and just wanted it to take care of any disasters). When I got back I couldn't believe how much growth there had been - every macro in the tank appeared to have been held back by nutrients far more than light. Since none of the major indicators (nitrites, nitrates, phosphates) has even registered on a test kit in quite a while, regardless of how I set the skimmer, it is going to get turned off for a few days / weeks / permanently.

Dave

 

[Ruu]

Skimmer has been off for 3 days now. Still no detectable nitrates or phosphates.

Dave

 

[sjvl51]

Plants need 2 things to grow - light and nutrients (otherwise known as iron, nitrites, nitrates, phosphates, etc). In most of our tanks, we do our best to reduce/eliminate nitrites, nitrates and phosphates. We use our macro algae to help in this reduction.

Basically, you had your macroalgae on a diet (low/no nutrients) and when you dialed back the skimmer, you took them off the diet.

Some people run their skimmers 24/7, others during the day or night only, others don't use a skimmer at all. All methods work, depending upon other factors.

Some things to consider -
Skimmers increase the oxygen content of the water which may make a difference depending upon your bioload. As the temp climbs, the O2 content goes down. Having a skimmer may help during the summer months when the temp may climb a few degrees.

Macroalgae remove certain nutrients. Skimmers remove other nutrients. They are not necessarily the same nutrients.

Macroalgae grow will be limited by the amount of one of the main nurtients. What I am saying is the all plants require certain basic nutrients. When any ONE of these disappears (is used up), then the macroalgae quits growing. This can trigger a sexual crash in the macroalgae.

I quote from Book of Coral Propagation by Anthony Calfo (p 201) "Regardless of where one stands in favor or disfavor of plant and algae growth in a reef system, there are some important facts to consider about the matter. First of all, many species of algae are known to give off noxious compounds that may inhibit the growth of corals and stress other invertebrates in the system. Secondly, as colonies of plants and algae grow larger each day, the demand for nutrients increases proportionately. If the ever-inceasing demand for necessary nutrients is not met, the colony can crash and die. ... I is believed that the regular clipping and harvesting of this vergetable matter from a system encourages even more vigorous growth, and the necessary cuts and incisions of the colony are known to leak noxious compounds to deter "predation". ... Many species of algae naturally have a short "lifespan". They have been observed in the wild and in aquaria to establish, grow quickly, and then suddently "sel-destruct". If the dissolution of the colony cannot be attributed to poor husbandry (water quality or lack of nutrients, for example), then it may have reached the end of its natural life cycle and executed a reporductive strategy. ... Caulerpa species that reach terminal mass and "self-destruct" leave behind a almost gelatinous mass. Caulerpa species are believed to be considerably more noxious than most algae in aquarium systems."

Food for thought - not to say what you are doing is wrong. I would expect little/no nitrates and phosphates when your macroalgae is multiplying this fast.

Vickie

 

[Ruu]

Totally agree (I thought the nutrient limiting was self-evident, but thanks for the additional information), and I was already harvesting regularly as I have experienced several mini-crashes in the past (with skimmer).

By way of an update, I did have to turn on my skimmer a couple of times in the last two days - not because of poor water quality (which still appears to be excellent, with no adverse signs on any of the life in the tank), but because I have a gorilla crab hitch-hiker who likes to dig. Skimming for a couple of hours really pulls the sand out of the water. I'll post the occasional update in here, just in case anyone cares.

Dave