Question about Cyanobacteria

[Aquaman]

I've have a 37 gallon tank setup with about 25 to 30lbs of rock, sump has a Berlin skimmer and a sedra 350 for return. the lights are brand new 55watt PC's The only inhabitant of this tank is a 3 to 4" dogface puffer. I do a 15 gallon water change each week since the puffer is a messy eater. But for some reason the sand and rock each day will be covered in cyanobacteria and after the lights go out each night the cyano almost completely disapear. only to start reapearing the following day.

All my water parameters are within normal ranges, nitrite, nitrate, amonia is 0, ph 8.3, alk and calc are fine.

I've run into cyanobacteria issues in the past and all were solved with water quality, current, even lighting changes. but I've never seen a case where the sand would completely cover in cyano only to disapear when the lights were out.

I have even reduced the lighting schedule but that doesn't seem to help. I thought that perhaps since I don't have that much rock in the tank their wasn't enough benifical bacteria so I added a gallons worth of Bio-balls to the sump about a week and half ago but i've not noticed any deviation from the routine.

Any hints to the cause of this constant algae bloom?

[Randy Holmes-Farley]

The cyano may be pulling nutrients out of detritus in the sand.

Have you measured tank phosphate?
Do you use carbon or skim to redcuce organics?

[Aquaman]

This is a new tank, freshly cycled, Sand was from a new bag, rinsed with RO/DI water and has a Berlin skimmer. Test kits have revealed 0 for phosphates, but the cyano could by absorbing it so nothing would show. It was suggested by a reefing friend that PH swings could cause the cyano to disappear while the lights were out.

[Bojan]

Originally posted by Aquaman It was suggested by a reefing friend that PH swings could cause the cyano to disappear while the lights were out. [/B] Interesting. How long lights have to be switched off. pH will drop if light is switched off.

Based on my experineces the following helps to eliminate cyano:
- strong water flow
- siphoning cyano every day,
- reduce PO4 and
- Anti RED.

[Aquaman]

Bojan, the cyano usually will be mostly gone by morning. So a full night cycle, 10pm to 10am. There is also a maxijet 1200 for water flow, so the tank has plenty of water circulation. I've been doing the 15 gal water change each week, which after done there is very little cyano in the tank.

I do not subscribe to the philosophy of dosing chems to get rid of cyano. I've dealt with cyano plenty of times in the past and know all the normal routines to rid the tank of cyano.

This is the first time I've ever seen a case where it would virtually vanish by morning and come back to cover the entire sand bed by the end of the day cycle.

Im confident I can rid the tank of the cyano, my question is more of what could cause the massive bloom/dieoff swings. If PH can do this how much of a swing is needed to cause this event.

Im out of town right now but first thing I will do upon returning home is put a spare PH monitor on the tank.

[Bojan]

Originally posted by Aquaman This is the first time I've ever seen a case where it would virtually vanish by morning and come back to cover the entire sand bed by the end of the day cycle. I had the same case 2 years ago. At that time I used Anti Red and eliminate cyano.

[Bojan]

Originally posted by Aquaman
Im confident I can rid the tank of the cyano, my question is more of what could cause the massive bloom/dieoff swings. If PH can do this how much of a swing is needed to cause this event. That is very interesting question.

Acctually I do not know is this realy massive bloom/dieoff swing. Are you sure that algae die during the night ?

Are you sure that pH do this?During the night , we have low pH in the aquarium.

[Aquaman]

I don't know that PH swings are causing this, it was a suggestion from a friend. The Cyano covers all the sand and rock with a light covering and is all gone except for a few small patches. I don't know that the cyano is dieing off, that is an assumption on my part, If I don't see it, where did it go?

I also added a carbon pad to help clean the water before hitting the skimmer. This is just a strange occurance.

[Aquaman]

Ok, PH swings aren't the cause, I got home yesterday at 6pm and tested, PH was 8.2 Got up at 6am this morning and tested again, PH was 8.0 Thats not enough a swing to cause cyano to vanish overnight.

[bertoni]

You might have a nocturnal predator that is consuming it. I've watched cerith snails at work on a microbial film of some sort. The ones I have work at night.