Diatoms and/or cyano..not sure...

[JT101]

I have an AquaPod 24 (enclosed hood) with the "standard" wattage PCs that come with this model (Model 7051).

I established the tank early June 2007 and it was fully cycled by the end of July.

I have been doing weekly 50%-70% NSW changes for months with no problems. However, I have very recently (within the last 2 weeks) seen a sudden growth of light brown algae (daitoms?) and sometimes purple algae (cyano?) on the sandbed. This stuff does NOT EVER seem to grow anywhere else, ONLY on the aragonite and NEVER in the shaded areas.

I have not changed my lighting schedule. Water levels are always excellent.

The only thing I can imagine is that there are phosphates in the water. I just read the other day that even absolutely pure natural seawater can have phosphates in it, yet artificial seawater has none.

My corals, shrimp and fish are all flourishing, eating and doing "excellently" but I am worried about the algae.

I have been very carefully scraping it off the sandbed each time I do a WC but it seems to grow back.

Admittedly, it seems to be SLOWLY growing less and less fast as it did when I first saw it but I am very curious as to its source.

Is it time to change my lights? They are not even 6 months old yet.

Any thoughts/advise would be appreciated.

Thanks
John

[lcstorc]

6 month old lights should be fine.
Is it growing in a low flow area? Try increasing the flow and reducing feedings. What is your source water? Try testing it for nitrates and phosphates. With that many water changes going on you shouldn't be having problems. What are you running for filtration? If it is the stock Aquapod have you taken out and/or washed the sponges in the back? Don't forget the one way down on the bottom of chamber 1.

[AQTCJAK]

the purple sounds like cyno however with your waer changes it seems to be caused by a flow issue. I would slow your feeding down as well if it continues to show up treat it with biyd enterprises chemi clean & do a water change 24 hours after the last treatment.

I would also cut back the amount of water changed per time you are removing alot of good bateria 40-60% of volume per month is fine

[justsunnie]

Are you using RO water? I was using conditioned tap for a while, cuz I got lazy, but once I switched back the 'toms went away. Also, you might want to cut back the amount of time you run the lights.

[JT101]

Originally Posted by lcstorc

6 month old lights should be fine.

Thanks, that's what I thought but I just wanted to make sure.

Originally Posted by lcstorc

Is it growing in a low flow area? Try increasing the flow and reducing feedings.

The flow thing is a little odd. I have seen this stuff growing in areas that are high AND low flow. I thought it was flow-related too but I have directed my Koralia Nano's directly towards the sandy areas that have the most growth and have not seen any change. What seems to be the biggest indicator is that it does NOT grow AT ALL in ANY shady areas on the sand regardless of flow - only where there is some direct PC light.

Originally Posted by lcstorc

What is your source water? Try testing it for nitrates and phosphates. With that many water changes going on you shouldn't be having problems.

My source is natural ocean water. Every time I test it for ammonia, nitrites and nitrates everything comes back zero. However, I have NEVER tested for phosphates. I need to get a kit and try that.

Originally Posted by lcstorc

What are you running for filtration? If it is the stock Aquapod have you taken out and/or washed the sponges in the back? Don't forget the one way down on the bottom of chamber 1.

No. I have several pounds of LR rubble in the back on both sides of that little "middle wall" in the back compartment. No bioballs or sponge media at all.

[JT101]

Originally Posted by justsunnie

Are you using RO water? I was using conditioned tap for a while, cuz I got lazy, but once I switched back the 'toms went away. Also, you might want to cut back the amount of time you run the lights.

No, just NSW changes. My tank hardly evaporates at all, so by the time any measureable amount is gone, it's time to do a large WC anyway, so addition of fresh water is a non-issue.

[JT101]

Originally Posted by AQTCJAK

the purple sounds like cyno however with your waer changes it seems to be caused by a flow issue. I would slow your feeding down as well if it continues to show up treat it with biyd enterprises chemi clean & do a water change 24 hours after the last treatment.

I would also cut back the amount of water changed per time you are removing alot of good bateria 40-60% of volume per month is fine

I tend to agree with that last statement, but since I am doing NSW changes, aren't I also ADDING a LOT of NEW bacteria every time I do a WC? BTW, I should add that even if I do the WC at night with just the lunars on, all of my corals open in full bloom right after the change - there must be something in that water they like.

[JT101]

How "agressive" should water flow be on an aragonite sand bed?

There is a fine line between "good enough" and so much that it blows all over the place.

Any recommendations?

[justsunnie]

I meant RO plus salt. We had a phosphate issue with the tap. Switched to RO salt, added some phosphate sponges, and the toms are gone for a couple months now.