Confused about Diatoms

[10" Red Devil]

Okay so I am really confused about Diatom. I have them in my established tank. It could be from feeding too much dry food. I know that they are caused by silicate in the water column. So I purchased a salifert silicate test kit (fresh will not expire till 2009). I tested my tank water, top off water (RODI fresh filters), Mixed Salt-water (contained in a 30 gallon rubbermade trash can from home depot with seio and heater) and there were no detectable levels of silicate! I then tested my tape water and there is a hair or trace of silicate in the tap water. Now I did a 50% water change with the same ph/temp/SG and about a couple days later the diatoms were back in full force! I also stopped feeding for a week after the water change. Prior to this water change I had not changed the water for a few months just so that you have everything you need to hopefully help.

Some tank specs:

Open Top 14 Gallon Biocube upgraded pump maxijet 900
Tunze nano Skimmer
Tunze Osmolator
Ebo Jager Heater
Pinpoint Ph monitor (just got it 1 week ago)
Milwaukee Refractometer for SG measurments
The first chamber is a refugium. It has been empty with the a 7 watt betta CF daylight lamp illuminated it for about 15hours a day. Been like that for a few weeks. I just added a large clump of chaeto about a week ago.

10lbs live rock
4" DSB with Oolitic Arragonite Sand
6 Nassarius Snails
3 Hemits
4 Astrea Snails
1 Clown
1 Green Banded Goby
1 Sexy Shrimp
Various Zoanthids
3 LPS
1 Photosynthetic Gorgonian
Sinularia
Misc Mushrooms

Interestingly all of my zoanthids have been closed for weeks now.

The tank is about 2 years old now. I am very unsure what to do at this point. Any advice is welcome!

My RODI water does read 5 with a MH-COM100 TDS meter but as I understand it since this is just measuring conductivity that this is as low as you can probably get your tap water TDS using this type of test? Anyway the Meter is brand new factory calibrated.

[moo0o]

you can have it read TDS instead of conductivity if you hold the....mode button

[10" Red Devil]

Originally posted by moo0o
you can have it read TDS instead of conductivity if you hold the....mode button

I was under the impression that it read the TDS using conductivity? Which only works with solids that can conduct or whatever (sorry I am not 100% on the science here) which means that you may still have dissolved solids in the water that are not being picked up by the meter. However this is the most accurate way that aquarist have for measuring TDS short of spending a small fortune on some lab grade thing.

[ClamIAm]

Did you look at them under a microscope to verify that they are diatoms? If there's no silica I don't see how they could be reproducing to noticeable levels. Diatoms are pretty much present in marine tanks all the time but they only bloom when nutrients are high, like when its cycling.

I'm not exactly sure what you should do about it. I usually find that microalgae blooms go away on their own unless there is a problem with the water quality. So if you did a 50% water change that should have helped.

[m2434]

What type of rock and sand, and where did you get it?

[Randy Holmes-Farley]

My RODI water does read 5 with a MH-COM100 TDS meter but as I understand it since this is just measuring conductivity that this is as low as you can probably get your tap water TDS using this type of test? Anyway the Meter is brand new factory calibrated.

If you are getting anything other than 0 or 1 ppm TDS from the DI, it is spent and silicate can be one of the first things to be released from a depleting DI.

I discuss those issues here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm


from it:

In the DI descriptions above, I did not address the fact that some ions will show a greater preference for attachment to the resin than will others. When the resins are not depleted, it does not matter what the ions’ affinity is, as all are bound. But in a depleted scenario, when there are more ions than ion binding sites, those with a higher affinity for the resin will be retained, and those with a lower affinity will be released. It turns out that silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.





and




Monitor the DI resins by measuring the effluent’s conductivity, either with an inline meter (set to its most sensitive level), or by measuring the effluent manually. If you are using a TDS or conductivity meter, then the measured value should drop to near zero, or maybe 0-1 ppm TDS or 0-1 mS/cm. Higher values indicate that something is not functioning properly, or that the DI resin is becoming saturated and needs replacement. That does not necessarily mean, however, that 2 ppm TDS water is not OK to use. But beware that the flow of impurities and the conductivity may begin to rise fairly sharply when the resin becomes saturated. Do not agonize over 1 ppm versus zero ppm. While pure water has a TDS well below 1 ppm, uncertainties from carbon dioxide in the air (which gets into the water and ionizes to provide some conductivity; about 0.7 mS/cm for saturation with normal levels of CO2, possibly higher indoors) and the conductivity/TDS meter itself may yield results of 1 or 2 ppm even from totally pure water by not being exactly zeroed properly. Also note that the first impurities to leave the DI resin as it becomes saturated may be things that you are particularly concerned with (such as ammonia if your water supply uses chloramine or silica if there is a lot in the source water).

[meg]

I also am having a diatom issue that I am sure is because of a depleted di resin. I have a dsb in a 120 with a 100 gallon sump and 20 gallon fuge with chaeto.
I am wondering the best course of action now. I changed the ro/di filters and have done one 65 gallon change with the better water. I am planning another 65 gallon change this week-end.
Do the diatoms fade away with water changes or is there something else I should do?
Thanks. I was searching for answers and ran across this thread.