It is update time:
I have made three changes.
First, I have removed cheato completely. Prolonged use of KZ ZEOzym, KZ cyanoclean and KZ Coral snow in my battle against cyanobacteria has taken its toll on my cheato. It has stopped growing. It is the first time since the early days of keeping my nano tank some six years ago that I have started to run a reef tank without macro algae. The impact of its absence is yet to be felt. I have moved all my live rock pieces, which were kept in the skimmer compartment of the sump, to where the cheato was kept. There is some nice sponge growth on some of the pieces.
Second, I have recently started to use a product designed to reduce nitrates and phosphates by actually adding nitrogen, phosphorus and organic carbon, along with some trace elements and potassium. What I use is called
Tropic Marin NP Bacto balance. The starting daily dose is 0.25 ml per 100 l. The maximum daily dose is 1 ml peer 100 l. I started very cautiously on 28th February with a daily starting dose of 0.1 ml per 100l. After one week I increased the daily dose to 0.16 ml per 100 l. I am now dosing 0.25 ml per 100 l daily. I will increase the daily dose only fractionally every two weeks from now on.
There is hardly any information and reviews about this product other than what is provided in marketing blurb on Topic Marin's website. I have managed to access to a German forum in which there was a thread on this product. After reading 47-page long threads, I was able to get in-depth analysis of the product by the proprietor, Herr Hans-Werner Balling, along with empirical data about the long term use of this product. Herr Balling emphasises the importance of maintaining a ratio of 10:1 between nitrates and phosphates. He argues that sudden removal of phosphates by GFO or other means causes not only STN/RTN on corals, but also cyanobacteria. I am yet to figure out why this is. My only guess is that unless there is sufficient nitrates in the water column bacterias' ability to consume phosphates in tandem with nitrates diminishes. What is interesting is that Herr Balling argues that so-called "nitrate limitation" cannot happen in reef tanks due to constant feeding of fish (unless there is carbon dosing). I am going to re-read the whole thread once again to assimilate his theories. I have no clue what my measurable phosphates are at present. I am going to order an Elos phosphate test kit soon. If Herr Balling is right and it turns out that nitrate-phosphate ratio in my tank is not 10:1, I may have to intervene by introducing additional nitrogen source to my tank (e.g. sodium nitrates). At present, I hardly get any nitrate readings on Salifert in spite of removing cheato.
Third, I replaced my Bubble Magus Nac 6a skimmer with a Deltec SC 1350 two weeks ago. I was not happy with the BM for a long time. My main gripe was that it did not produce consistent foam head. After reading a thread on RC and getting advice from @Sahin, I removed its bubble plate and cup. It improved but its skimmate production was still not consistent. I then questioned whether or not this skimmer's neck size was too big for the nutrient load of my tank (read this as was it too big for my tank). I sought help from a fellow reefer, @rishma, here on RC. He provided some visible metrics to evaluate the appropriateness of a skimmer:
"
Here are my current thoughts on skimmer sizing (assumes well designed skimmers with balanced air/water and neck diameter):
Perfect Sizing: A perfectly sized skimmer is probably not realisitc, but it is a good starting point. This skimmer would skim consistently and remove waste down to the acceptable levels at the same rate waste is introduced to the tank. Little to no adjustment required, set it and forget it. A perfectly sized skimmer would never be idle, but would be close.
Undersized: Skims consistently with little to no adjustment but waste builds up in the tank water and the skimmer cannot keep up.
Slightly oversized: Skims well most of the time but goes idle when waste levels drop below the amount that can form a stable foam head in that neck diameter. Requires adjustments to keep skimming consistently and likley skims wet. With adjustment, it will maintain low waste levels in tank but not as low as the "Perfect Size".
Grossly oversized: May skim when first broken-in if waste levels are high enough, but strips the water quickly to the a waste level that cannot maintain a stable foam head. Very frequent adjustments to keep it skimming and it will skim wet. Remaining waste level in tank can be an unacceptably high in concentration.
So how to get a perfectly sized skimmer? Its probably not possible"
The BM skimmer definitely exhibited signs of being a "slightly oversized" skimmer. On the other hand, the new Deltec SC 1350 appears to work flawlessly, producing consistent foam head without requiring any adjustments. According to @rishma's definitions, it is either "perfect" or "slightly undersized", but it is definitely not "slightly oversized". Future measurements on nutrients will confirm one way or the other what type of skimmer it is for sure.
I have built a platform to raise it so that it sits in 8" of water depth.
It seems to be skimming quite dry despite the fact that the water outlet is almost closed. As you can see, the foam does not drain but kind of "hangs", which I am not mistaken is an indication of dry skimming. I may attempt to tinker with the water level in the future, so that I will get wetter skimmate, but will leave everything as is.
Finally, here are some photos, which I took last night. Everything is OK except cyanobacteria. Corals are growing, their polyps are extended and their colours are OK. I am fairly happy overall.
