The Digital-Reefs Black Tank – Passing 6 Months

As we pass the 6 month milestone, it’s time for another update on the Digital-Reefs test tank. As ever, we’ve been tinkering with this, and fiddling with that, to ensure the system continues to run as smoothly as possible… and of course biologically the tank continues to evolve.

But first, let’s talk about equipment. If you’ve been following our previous entries, you’ll know that in our last piece at 2 months old, we’d recently added a gravity fed Calcium reactor as new coral stock was introduced. This complimented a conical protein skimmer, Chaetomorpha refugium and Biophos in a TMC Bio React 500. This arrangement has continued to provide for basic life support very well over the last few months with nutrient levels staying low and mineral levels within target ranges. With this foundation in place, we went on to add GAC into the equation and for this settled on Vertex’s ROX carbon. Although we’ve previously run this in a reactor, we’ve now settled on using it in a fine mesh bag attached to the outlet of the TMC reactor. This isn’t the most elegant solution but certainly does the job. Typically we are replacing the GFO once every 6 weeks and the GAC once a month. In addition we have water changes of course. For this we are still using ReefCrystals and typically changing out about 5% every couple of weeks, vacuuming detritus from the sump rather than from the main tank. We also clean our skimmer cup and replace the filter sock regularly. We’ve made one or two little ‘tweaks’ also. Firstly, as mentioned in our last entry we’ve been using a modified Eheim Liquidoser to deliver coral foods during the night to the tank (once every few days). Well, we are also using this to deliver a second flake feed in the middle of the day when we are not normally around to tend to the tank. Overall its proven to be a really useful piece of kit. In terms of feeding, we’ve also modified our ‘bog-standard’ algae clip by supergluing it to a bracket, which allows it to be slotted onto our eurobracing. This means that we don’t have to put our fingers in the tank when we want to add Nori. Feeding several different types of flake food, we got sick of having big stack of pots in the cabinet too and as such, took 5 minutes to make a mixture of all the different flakes in a single pot. Although not perhaps ‘ground-breaking’ developments these measures shave valuable minutes off regular maintenance tasks with the added bonus of benefitting livestock. Finally we’ve replaced our 25 litre top-up bucket with a 30 litre bucket which means we get pretty much a full week between refills, oh and we refreshed the DI resin in our RO/DI unit as the TDS had started to creep up a little. Probably the biggest development is that we’ve switched our cone skimmer for a recirculating model. Now, we didn’t do this because we were unhappy with the cone skimmer, rather we just wanted to try a slightly different method. Now running for around 3 weeks, we’ve not noticed any major changes yet, but there are certainly a few subtle indications that this new skimmer may be influencing conditions. We’ll be bringing you a review on the new skimmer very shortly… once we’ve had a little more time to evaluate it. So that’s really all that’s changed technology-wise.

Biologically, the system has also continued to mature and we haven’t noticed any more ‘blooms’ in microfauna populations indeed general ‘pod’ levels seem to have fallen off to background levels. We still see life in the sump but there are very few tiny organisms evident in the main tank (which, frankly we don’t mind). We have added a thin layer of fine sand into the refugium section of the sump primarily for the benefit of our Edible Sea Cucumber which we are nursing back to health. ‘Mr Blobby’ as he is affectionately known certainly looks much better than when we moved him over and seems to enjoy feeding on the fine layer of mulm that accumulates primarily in the skimmer and fuge chambers. He looks double the size he did originally. Talking about Chaeto, we’ve harvested this a couple of times since the last entry, each time removing about 50% of the clump (an amount which easily fills a 2 litre jug). Moving up to the main tank, we’ve added a few more corals and fish recently. Coral-wise, we added several frags specifically Superman, Rainbow, Jedi Mind Trick, and Silver undata encrusting Montipora sp., plus 2 more Acropora sp. including a blue A. turaki. We also added 3 plating Montipora sp. – green, purple and orange. We also recently added a large purple chalice coral and a deepwater tabling Acropora. All seem to have settled in nicely and our existing corals are all still OK and showing growth. Some have intensfied in colour while others have perhaps faded a little… some have grown a lot, some only a little. Take a look at the shots below for some of our new stock and some side-by-side comparisons of established colonies.

Onto fish now, and we’ve increased our stock a fair amount since the last entry where we had a Yellow Tang, Starcks Damsel, Percula Clown, Flame Angel and Scarlet Hawkfish. We’ve still got all these fish and we’ve now added a stunning Hoevens Wrasse, a juvenile Midas Blenny, 1 white watchman goby, 1 yellow watchman goby and a Royal Gramma. Now in the tank for around 5 weeks they have all settled apart from the Royal Gramma which unfortunately died around 2 weeks after being added. We’ve no idea why this happened… once day she was feeding openly the next day she retreated to her cave and was obviously exhibiting laboured breathing. She was also generally unresponsive to the point where we were able to waft her out of the cave and then extract her gently with a pair of tweezers to the sump. Unfortunately she died a day later… a disappointing development but at least we managed to get her out immediately after death. In another development we miraculously captured the smaller YWG with a net after it was evicted by the larger WWG and put it in the sump. We had hoped that they may pair up but it seems that the Yellow individual may not be mature or strong enough yet. We hope to condition him in the sump and then try a reintroduction in the future. The white watchman (who we assume is a female) looks happy in the main tank anyway and has teamed up with our Tiger Pistol Shrimp. We have an amazing story about this shrimp actually…. when we remove our filter sock we normally just give it a rinse under the tap, rubbing it to dislodge any sludge, and then we put it out to dry while we replace it with a previously dried sock. However after rinsing the sock on one occasion we were alarmed to suddenly discover that the pistol shrimp was in it! Amazingly, the shrimp must have got over the weir in the night (the weir is covered with egg-crate by the way) and descended into the sock. Fearing the worst we quickly plopped the unhappy crustacean back into the display where it came to rest on the substrate, twitching and convulsing. To be honest we were sure it wouldn’t survive. Miraculously though, over the next hour or so, the shrimp righted itself and then crawled to a nearby rock, still apparently dazed. Despite all odds, a few days alter is was apparently fully recovered and back to its enthusiastic excavations. The moral of this tale?… always check your sock before you stick it under the tap! On the subject of sand sifters, we’ve added 2 strawberry lipped conches to compliment the 4 conehead snails we have.

So that’s where we stand today. In the coming months we are hoping to see our corals continue to ‘fill out’ and we’ll be modifying the aquascape as we see fit. We’ll aslo be changing a couple of light tubes, diversifying our clean-up crew and continuing to test some interesting new equipment!


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