Diatoms?: how to proceed  8/23/07
Dear Crew,
<Mark>
I know the information is on your web page; I just can't seem to put it all together.
Tank parameters:
90gal set up for 3 years. Have always seemed to have an algae problem of one kind or another since automatic fish feeder fell in the tank while I was at work 1.5 years ago.
Water flow is approximately 1500 gph
Filtration: sand and protein skimmer
pH 8.2-8.4
NH3=0
NH2=0
Alk=9dKH
NO3=undetectable with Aquarium Pharm.
PO3=undetectable with Aquarium Pharm.
Calcium=400ppm
5 gallon water changes weekly
Livestock:
4" yellow tang
3" flame angel
2" cleaner shrimp
2 species of Montipora
3 species of Acropora
2 species of star polyps
1 frogspawn colony
Three weeks ago I added Kalkwasser to replace evaporation since my calcium levels were a little low (350ppm vs. the 400ppm as present). Two days after I added the Kalkwasser I noticed my BGA was replaced by what I believe to be diatoms (I looked at them with a microscope and found they were too large to be BGA, but did not appear as symmetrical as I would expect from diatoms.
<Bacillariophyceans are distinctive... as you state>
Cells were oval shaped with only one plane of symmetry).
<Not diatoms. Were organelles, nuclei apparent?>
Also, many of them float to the water's surface during the day; less or not at all at night.
The SPS don't seem to be affected but the frogspawn and star polyps don't look very good (stay closed most of the day).
<Yikes...>
In an effort to rid my tank of this bloom I replaced my DIY protein skimmer with a Tunze DOC 9005, added an inch of 1-3mm aragonite sand (it was down to 2.5), and switched from tap water to RO that I buy from the LFS. I also added a small clump of Chaetophora to my tank.
<Really? Am assuming you mean/t the genus Chaetomorpha>
What should my next step be? Keep up with the water changes and wait it out?
<Yes, I would... unless the Stony Corals continue to "look bad"... in which case I'd effect another, larger water change and use carbon in your filter flow path>
Buy some new live rock and/or order live sand activator to recharge my system with small detritivores?
<Also a good move>
Was this caused by the CaOH precipitating PO3 thus killing the BGA and leading to a diatom bloom?
<Possibly... but not diatoms... some other Protista>
Thanks for a wonderful website,
Mark
<Do send along pix if you can. Bob Fenner>

Re: Diatoms?: how to proceed   8/24/07
Hi Bob,
<Mark>
Thanks for your quick reply. I forgot to mention that I also stopped adding Kalkwasser a few days ago. As a result the pH in my tank reverted to pre-Kalkwasser readings: 7.8 in the morning and 8.2 in the afternoon. Also my calcium increased to 420ppm. This could be due to experimental error (difference in reading of only one drop) or due to increase calcium solubility in the lower pH.
<Better to look into bolstering alkalinity slowly through your water changes over time here...>
The corals do look a little better today, but I am concerned about this Protist bloom. I looked at a sample I took from the bottom of the tank (first time was from top/dead) and found that when alive they are very mobile.
<NOT Diatoms...>
It looks like they use cilia for locomotion. Also they seem to contain brown chloroplasts and a nucleus. Enclosed is a Word document with a picture pasted onto it. Are there any good herbivores for this?
<I see... more likely Dinoflagellates...>
I am afraid to buy fresh live rock at this point because I think it would become smothered.
<Mmmm>
Thanks,
Mark
P.S. I did mean Chaetomorpha (not Chaetophora)
<Ah, good. Bob Fenner>

Re: Diatoms?: how to proceed... Maybe Euglenoids    7/25/07
Hi Bob,
Just wanted to thank you for your help. I did some searching and it looks like these are Euglenoids from the genus Trachelomonas
(though from what I've seen on the internet this is mostly a freshwater genus). The following link convinced me; especially the movement.
http://images.google.com/imgres?imgurl=http://silicasecchidisk.conncoll.edu/Pics/Other%2520Algae/Other_jpegs/Trachelomonas1.jpg&imgrefurl= http://silicasecchidisk.conncoll.edu/LucidKeys/Carolina_Key/html/
Trachelomonas_Main.html&h=235&w=288&sz=38&hl=en&start=27&tbnid=H0z0lEYVy3pntM:&tbnh=94&tbnw=115
&prev=/images%3Fq%3DEuglenoids%26start%3D20%26gbv%3D2%26ndsp%3D20%26svnum%3D10%26hl%3Den%26sa%3DN
<Okay>
So eventually the alkalinity will improve with water changes?
<Mmm, yes... should... with higher alkalinity in the new water...>
I've had low pH (7.8-8.2) for at least 1.5 years with weekly water changes. Of course the addition of the Tunze skimmer may take some pressure off the buffers in the saltwater mix (Instant Ocean).
Thanks again,
Mark
<I would look into supplemental bolstering of your alkalinity here... Bob Fenner>