# GDA/BBA relation to GH, KH, or PO4?



## DMtankd (Dec 20, 2009)

Hi All,

I was recently successful in ridding my tank of GDA and, based on the (non scientific) way I was able to get rid of GDA, I have a hypothesis that I would like to test out. I would like to get some input from others who are experiencing these two kinds of algae.

The hypothesis: 
GDA is more prevelant in tanks with high GH, KH, or Phosphate levels (not necessarily all 3). 
BBA is more prevelant in tanks with low GH, KH, or Phosphate levels (not necessarily all 3).

Let's say "high" is > 6gh, 2kh, and .25ppm Phosphate. And "low" is less than these values.

If you've got experience that supports or refutes this, I would really appreciate hearing your input.

Just for reference, here is what I did to beat GDA and the source for this hypothesis:

I had a terrible case of GDA in a tank for a number of months. Within a week of scraping, all glass would be completely covered again. I had never seen even a hint of BBA in this tank. Its a CO2 injected tank with 2 T5HO bulbs about 8 inches above the waterline. After trying all manner of variations in my macro/micro levels, the 'wait and pray' method, and reducing my lighting to no avail I was pondering tearing down the tank. I decided to try one last measure - using RO water for water changes instead of tap and reducing my phosphate dosing.

I did water changes with 90 percent RO water and 10 percent tap and reduced the phosphate in my dosing regime by about 80 percent.

Tap water here is hard (about 10 - 12 gh and 3-4 kh). Based on water company reports (and corroborated by my test kits) the gh was about 3:1 Ca to Mg. The only other standout about the tap water that I am aware of is that it contains about 1 to 1.5 ppm Phosphate. With my dosing, I was adding additional phosphate and so the tank levels were always at or above 1ppm Phosphate. Nitrates in the tank averaged about 10ppm based on calibrated test kits. I don't have calibrated kits for other micros/macros, so I wont state their levels, but I did have strong growth and pearling, so I am making an assumption that levels of other ferts were OK.

The impacts of my switch to RO water and reducing my phosphate dosing, that I am aware of, were:
gh went from 10-12 to about 5-6
kh went from 3-4 to about 2-3
Phospahte went from >1 to <.25

Within two weeks of keeping the tank at these new levels, I had no visible GDA on the glass. However, within about 3 weeks, I saw my first signs of BBA ever in this tank. Nothing else about the tank parameters changed at all that I am aware of (and I monitor things pretty closely).

It has been a number of months now at these levels with no recurrence at all of GDA. I treat the BBA by keeping the DOC low and spot treating with Excel every now and again. 

When I get tired of all the extra time I've gained by not doing weekly battle with the green curtain, I may try reverting to tap water only / high phosphates to see if GDA pops up again and confirms my hypothesis. In the mean time, I'm hoping this poll might shed some light.

Dan


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## darkoon (Jun 7, 2010)

interesting... you finding matches with what Christian_rubilar stated in his Method of Controlled Imbalances thread,
"The 4:1 ratio Ca:Mg cannot be sucesfully use under water. When there is too much Po4 in the water and you have an imbalance in the Ca:Mg ratio, you will have GDA. "
it would be interesting to see if you add more PO4, would that cause GDA to come back, and/or when you go back to your tap water, would GDA come back.


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## Bert H (Mar 2, 2004)

Interesting observation. Unfortunately, I cannot really give any input directly to it. But, I do have very hard water (gh12-13), (kh 9-10). Except for a brief episode one time on one tank, I've never had real issues with it.


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## darkoon (Jun 7, 2010)

according to MCI, too much PO4 and imbalance in Ca to Mg ratio cause GDA, do you know what Ca/Mg ratio of your tap water is?


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## DMtankd (Dec 20, 2009)

Bert, thanks for the input. Just to confirm, you briefly had an outbreak of GDA or BBA?

darkoon, christian rubilar's MCI thread was actually the key reason that I tried the switch to RO and dropping the phosphate dosing. It was a very helpful thread that really helped me to step back and evaluate the needs of my own specific tank and tweak some parameters (Ca and Mg) that I hadnt really considered before. My tap water is about 3 to 1 Ca to Mg. I neglected to add in my first post that I did start adding a bit of Mg at water changes at the same time that I switched to RO water. The amount that I added was minimal and didnt change my Ca to Mg ratio that substantially. I intended to increase my Mg dosing as an additional measure if the RO & phosphate dosing reduction didnt work, but it didnt come to that.


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## Bert H (Mar 2, 2004)

> Bert, thanks for the input. Just to confirm, you briefly had an outbreak of GDA or BBA?


Sorry, it was GDA.


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## bosmahe1 (May 14, 2005)

I kind of, have my doubts on that finding. I use only tap water with a GH of 7 to 8 and a KH of 4. I did have GDA for awhile but didn't really make any changes except scrape and suck it out at 50 % water changes. The GDA disappeared as the BBA reappeared. My guess is that there was competition of the algaes. I've always had issues with BBA and the only thing that seemed to help is reduce the lighting. I currently use 2 x 39 watt T5HO over a 58 gallon for 8 hours. Increasing or decreasing phosphates or other ferts has never helped me. I usually went the EI route but, have been using PPS pro with 50 % water changes for a few months and that hasn't changed anything either. My CO2 is tweaked to where the fish are breathing a little heavier than when they don't have CO2. The 4 kdh drop checker is more yellow than green. My water is medium hard so, I would say that BBA has no problem with hard water.


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## DMtankd (Dec 20, 2009)

That is interesting that you say the GDA disappeared as the BBA reappeared.


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## darkoon (Jun 7, 2010)

i had pretty bad GDA in my 10g, and some GSA too when I was easy on ferts, after I doubled the dosage, them seem to have stopped development.


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## carlschr (Nov 10, 2008)

Interesting. We use water from a water softener and we never have green dust algae but we always have a little BBA. That matches your hypothesis. However, the plural of anecdotes is not data...


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