Another "Help me! Algae!" post: GSA (warning, it's LONG)


Guru Class Expert
Jun 26, 2008
Albany, California
This may be a little long but I want to give my recent background attempts
to help figure out what I should do now....

Ok, well I thought I had things under control. First it was BBA in the past
and again about 2 months ago, that now seems to be defeated and is almost nonexistent.

Then GSA started showing up. I seemed to get that slowing and even receding until the last
3-4 days, and in the last 2 an explosion of GSA everywhere and even GDA on the glass. See attached photos of the GSA.

Here's the (long) but total story since my move from a lower tech,
non-CO2 tank to pressurized, EI dosing, higher light tank about 2+
months ago:

About 8 weeks or so ago I went from a CF 2watt/gal setup with no CO2
and dosing Excel and Flourish (no macros) in my 72 gal to a Hagen T5 HO
54watt x 4 set up with pressurized CO2 and dosing macros and
micros (dry ferts) following the EI method for a 60-80 gal tank. I have
had an Eheim 2028 going on this tank for the last year.

I had decent growth for some things over the first 10 months with
this tank (bought and set up last summer) as a lower tech tank but not
all plants grew well. Sort of a mix, java ferns and other slower
growers (anuibias) just seemed to stagnate and get algae everywhere
(though many tell me they are fool-proof, even with this fool?) but cabomba,
pennywort, myrio, tiger lotus and some bacopa grew well for me while many
of the bulb type long-leaf types, swords and any other plants needing higher light
either melted away or just sat there barely growing. In this low-tech
tank I had some pretty bad BBA issues which I fought off at first with
syringe squirts of H2O2 and excel but it soon took over and since I was pretty
much on my own (had not even tapped into any of these online forums
yet and really knew nothing about a planted tank other than what the
slackers at the nearby LFS told me---just dose excel and flourish) I
just took the algae as what happens in a planted tank. The BBA was all
over, as was the occasional hair algae and GSA. The BBA covered my
three big pieces of driftwood like a fur coat and on a lot of my
plants on the older leaves it was BBA and GSA galore.

I started getting itchy a couple months ago to do more for my tank as
although the stem types were growing well they would quickly get algae
amongst even on leaves only 1 week old. I also wanted to go more
high-tech to grow more colorful plants and have a brighter aquarium.
I also started to realize I needed to get some strong plants growing
and to expand my ferts so as to out compete the algae.

I then attended my first meeting of the San Francisco Bay Area Aquatic Plant
Society ( back in April. There I learned what I
was not doing right, what was likely causing my issues, why I should
consider CO2 and EI of bulk dry ferts, and so forth. Also got some really cool
plants from the swap table and I was determined to get those to grow!

So, I went the route of getting pressurized CO2 and the better lights
as I mentioned above and I started learning about better fert dosing
regimes. Based on the difference in brightness from my earlier light
set (4x36 watt CF) to these T5 HO's I'd say that although on paper
it's now 3w/gal I think it's more like 4+ watts/gal based on lumens
hitting the bottom of the tank as these lights seem MUCH brighter than
my older CF one.

I then, along with all this, decided to do a MAJOR re-scape and also
pretty much start-over, taking all the driftwood out, soaking it in
H2O2 and Excel, letting it dry out completely for a week, removing
almost all plants and pruning of ALL leaves with any evidence of algae
at all, and then putting a layer of Soilmaster Select on top of the
sand/red flourite substrate I already had there. I then replanted
everything, got the CO2 going, the better lights and started a PMDD
dosing regime, and for a couple weeks things looked good until the BBA
started showing up again!

I then got a hold of one of those 2" PVC in-line CO2 reactors and got
a second eheim (a 2026) in which I installed in-line that reactor.
Wow! The tank, which I thought was pretty clean and clear, all of a
sudden became CRYSTAL clear with the two eheims running.
Over-filtering is NOT over-rated! I highly recommend it! This also
helped with more flow and water movement, which I was quickly
realizing was VERY important to ensure proper CO2 coverage around the
tank. I also got a drop checker and using 4dKH water found it to stay lime
green so my bubbles per second (about 3-4) and my reactor seemed to be working.

For the next week or so everything grew like mad. Anubias were
pumping out a new leaf a week, my Ludwigia, which barely survived and
grew very poorly in the old low-tech tank, took off like a rocket and
the leaves become a rich red, my tiger lotus leaves doubled in size
and growth rate, crypts were really taken off and ones which were
green previously were now coming out reddish bronze..... Interestingly
though things that grew SO well in the low-tech all of a sudden
stalled out: my pennywort, cabomba and myrio were hardly growing at
all and some were turning white!

For another week things looked good though I did see small signs of
BBA and GSA I trimmed every night figuring this must be remnants from
earlier bad algae issues. However then I started to see BBA growing
again on the driftwood. So, I'd come home from work every night and
trim where ever BBA was making it's small but definite comeback or
spot treated H2O2 or Excel with a syringe on driftwood, crypt leaves
(the tips) and the rhizomes and roots of the anubias. I then did
3 days of 5x normal overdosing of the whole tank with Excel. That
may have been what it took but the BBA seems to almost come to a huge
halt. I still saw a little BBA on the anubias and the tiniest bit on
the crypt leaves but the small tufts that started growing on the
driftwood stopped as did most of the BBA growth on anubias rhizomes.
I did however start to see GSA more on the glass and on older leaves
of a lot of stuff.

After researching here and elsewhere I read that GSA is almost always
from too little phosphates and too little CO2. Well, with the two
eheim spray bars and a Koralia 1 to add to my water flow plus my drop checker
with 4dKH water showing lime green I figure my CO2 must be fine. In terms of
my phosphate and other macros using both API and Seachem phosphate test
kits it appears my phosphates are over 5 ppm. My nitrate test kits show me at 20ppm+.
I do have a heavy fish load, probably about 20% more than I should have if you follow
the 1" per gallon rule but with the two eheims and 50% water changes per week
I figure I'm mostly on top of that. Despite my test kits showing fairly high phosphates
and nitrates I decided about a month ago to do a straight EI dosing anyway.

Since my tank is a 72 gal for EI I'm doing 3/4 t. of KNO3, 3 ml of Fleet and 1/4 t. of
K2SO4 on my water change day (after the change) alternating every other day (total 3x a week)
and on alternate days opposite to the macro dosing days I am dosing 1/4 t. of CSM+B
for a total of 3x a week. I also add 1 T. of GH Booster on water change day too.
This way I figured I cannot possibly be deficient on my macros or micros, my CO2
is strong and seemingly be distributed around the tank well. I also backed off my
lighting from 10 hours a day to 8 hours and raised my light a few inches above the water.

For a few weeks after this the BBA stayed in check and it even seemed the GSA was
not increasing much. About once a week I'd see a few spots of GSA and what may be
GDA on my glass but it is so minimal that a quick and easy scrape eliminates it without a problem.

Then about 3-4 days ago I notice the top leaves of my Hygro are getting a lot of GSA
(see photos attached) and it also was starting to grow on some new Tonina I just got
5 days prior! Then last night it was showing up in many places and is really strongly on
the glass as never before. The only thing I changed in the last week was to replace one
of my 4 T5 Life Glo bulbs (6700k) with a Pro Glo (18,000k) bulb as some people mentioned
it's a nice mix and helps accentuate red in the plants.

I am really bummed about this GSA as so many people say 99% of the time it's due to CO2
shortage or insufficient phosphate. But I cannot see how I could add more CO2 nor more
phosphate. Any thoughts or radical ideas for me??

Thanks for anyone's help here, sorry for the long post.


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
I think you have much too much light. T5HO bulbs are very bright bulbs compared to PC bulbs, so I think you are correct in believing that you have the equivalent of much more than 3 watts per gallon. Avoiding algae with that much light will be difficult, no matter what you do. So, I suggest that you start by either raising those lights about 6 inches, or just removing at least one bulb from the lights.

Now, things should go enough slower that you have a chance to figure out and tweak things to get the algae under control. Also, the demand for CO2 will be less, so water circulation issues will be much less.


Lifetime Charter Member
Lifetime Member
Mar 21, 2005
Additionally to what Hoppy suggests, try doubling your PO4 dosage and adding a little bit more CO2. GSA always ignore hobby grade test kit readings and so should you. :rolleyes: Have you considered the possibility that the test kit readings may be false? In fact, PO4 test kits are notorious for their inaccuracy and/or inconsistency.

Also you have more plant mass due to growth which means that the nutrient uptake demand has increased from when you first started.



Guru Class Expert
Jun 26, 2008
Albany, California
Thanks Hoppy and Ceg for plowing through my rambing post and commenting with your thoughts. It's my attempt to journal what I've done the last 2 months or so in the hopes of figuring out what's going on. Reading your thoughts and re-reading some of Tom's on such subject (and how he says 95% of the time it's CO2) I have cranked up the CO2 a bit and doubled the phosphate dosing to 6 ml 2x a week (and added an additional 1/8 t. to my N and K macro dosing days too---so now it's 7/8 t. of KNO3 and 3/8 t. of K2SO4 on the macros days). Since I have only limited experience in getting a tank heavily growing I may be short of these macros due to heavy plant load and not realize it.

Further I went and changed my lighting somewhat figuring as Hoppy mentioned my really bright lighting may be causing the algae or helping it along. It turns out though that my 2-bulb (2 x 54w) Hagen T5 HO fixture will only light up if both bulbs are installed. Remove one then plug it back in and the other flashes on and then turns off within seconds. Seems only using one bulb in the fixture is not possible. So what I did instead is I left one of the 2-bulb (2 x 54W) T5 HO fixtures over my tank and got my older 4 x 36W PC fixture from the garage and put it on the tank in place of the other T5 fixture. As I mentioned even though this is in theory 144W it is about 30-40% less bright to my eye than the just one of the 2-bulb (2 x 54W) T5 HO fixtures. I put the T5 one in front over the low foreground plants figuring they will need the stronger lighting to reach the substrate and put the PC fixture in the back over my taller background plants. To my eye this appears to be about 25% less light on the tank overall.

Will try this for a few weeks and see what happens.

Tom Barr

Staff member
Jan 23, 2005
Rich, if you are coming to this Sat's open house, we can talk about it in person etc.
Be far more helpful than anything here.

Tom Barr


Guru Class Expert
Jun 26, 2008
Albany, California
Tom Barr;28042 said:
Rich, if you are coming to this Sat's open house, we can talk about it in person etc.
Be far more helpful than anything here.

Tom Barr

I will be there. Thanks. Look forward to meeting you and the others. See you then.