Persistent diatom issues - confused about fertilization regime... - The Planted Tank Forum
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post #1 of 4 (permalink) Old 04-25-2015, 08:05 PM Thread Starter
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Persistent diatom issues - confused about fertilization regime...

Hi all - been lurking for a while. As the title says, I have battled a persistent diatom problem in my high-tech 7.5 gallon since start-up, and was hoping you lovely people might be able to offer some insight Iím also very confused about fertilization. Waffled a bit as to whether I should post this here or in the ferts section, sorry about that.

Also pardon my rambling as I try to fit all of the pertinent information, and everything that I have noticed over the past four months, into a single post. Let me know if you have any questions or need more info!

Imgur album with recent pics:

Iím sort of new to the planted tank world, and this tank feels like one big experiment with balancing ferts - lighting - CO2. It has been set up since the beginning of January, and cycled quickly with filter media from my first low-tech tank, but I have been arguing with diatoms all throughout. I know they can be an issue for a couple months after the cycle completes, but now I'm just frustrated and donít really know what direction to take with it, hah. My major source of confusion is lighting and fertilization. I donít understand whether I *should* be dosing ferts to combat algae, or not dosing ferts, as I have heard both stances. At first, I went with the former:

Up until the beginning of April, I had been using dry ferts; NPK & Plantex CSM+B, at about 1/3 the recommended EI dosages. The light (Finnex Planted+) was on for 6 hours a day, and CO2 came on and turned off two hours before. I had some dust algae, which did its thing and went away, but cyano and diatoms would just *not let up*. My plants were growing well enough, but the Ďalgaeí kept spreading. I did 50% water changes twice a week.

The tank was/is home to a single betta fish. Plants are rotala rotundifolia and s.repens. The feesh in question is fed two or three pellets once a day.

Parameters/etc. around mid-March -
Tank size: 7.5g
Lighting: Finnex Planted+, on for 6 hours/day
Substrate: Fluorite black sand
Filter: AquaClear 20
CO2: Pressurized CO2 at 3bmp-ish; turns on/off two hours before the lights. Iím using a fluval diffuser and bubble counter.
Fertilization: Seachem root tabs; 1/3 EI, dosage figured through Macros and plantex 3x/week on alternate days.
Water change: 50% twice a week
Nitrite: 0
Ammonia: 0
Nitrate: at least 80 (was not expecting! Geez.)
Phosphate: 1.0
pH: ~7.0
gH: 8.0

But then I went on vacation at the end of March. For that week, I reduced the lighting to 3 hours/day (brought the lighting down over the course of a couple weeks, and adjusted CO2 as well), and the plants went without their daily dosing of dry ferts. I was expecting some horrible algae explosion, but when I got home, I had managed to kill off the cyano (yay!), and while I still had diatoms, they at least hadn't taken over to the extend I was envisioning. So now Iíve kept the 3 hour/day schedule, and am only dosing Seachem Potassium twice a week. The diatoms are starting to creep back with more enthusiasm, however, which has led me to writing this post

I think what I am mostly confused about is how to handle ferts and get these diatoms under control. When I was dosing at 1/3 EI and 6 hours of light, I had major issues with cyano and diatoms, but was trying very hard to just push through it, hoping everything would come together eventually. Again, I have heard that dosing excess ferts causes algae, and I have heard the opposite. So I feel like Iím missing something. Longer photoperiod + fertilize? Longer photoperiod hold the ferts? Maybe with 1/3 EI, it was still too much. Whenever I trim or replant the rotala, new growth has always appeared small and leggy - not very bushy at all. Is it a light issue? They donít look ďstuntedĒ as if it were a nitrogen problem. JustÖvery small leaves. This was also the case while I dosed 1/3 EI. Iím stumped.

Currently -
Lighting: Still the Finnex Planted+, now on for 3 hours/day
CO2: 3bmp-ish; turns on two hours before the lights, and off one hour before
Fertilization: Seachem root tabs, 1.5mL Seachem Potassium twice a week
Water change: 25% weekly
Nitrite / Ammonia: 0
Nitrate: 20.0
Phosphate: 1.0
pH: ~7.0
gH: 8.0
kH: ???

The nitrate:phosphate ratio has stayed the same for the last two weeks. Not sure if I should try to up the phosphate to 2.0, or decrease nitrate to 10 (10:1 ratio, am I doing that right?). I have one or two dots of GSA, but nothing too exciting.

Thanks for reading, and any + all suggestions!
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post #2 of 4 (permalink) Old 04-27-2015, 02:27 PM
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It is natural to think that excess nutrients will cause algae, but it is probably more accurate to say that an imbalance of nutrients will cause algae.
Now that your tank is more mature (and seeing how good your plants are doing based on the pictures), I would focus on the needs of the plants now, and not worry about algae (more on that soon). Resume dosing (or at least some micros and a bit more phosphates), provide a longer photo period, maintain the CO2 levels, and change the water at 50% again. All of these should have a positive impact on the plants, and not encourage any new algae (ie GSA).

It is likely the BGA (cyano) was a result of early cycling (presence of ammonia?), and should not return.
Now the diatoms are another issue. They are very successful at scavenging low levels of nutrients and light. You are not going to 'starve' them by lean dosing or a short photo period. You often hear that they will go away after the tank matures. From papers I've read, one theory is that they are eventually 'out competed' by green algae when the latter finally establishes itself in the tank. The green algae requires more intense light than diatoms. So one method of attack is to increase light intensity. This approach is dangerous if you don't give your plants what they need in terms of nutrients and CO2, because the intense light will increase the demand of both, and if not provided will lead to other forms of algae that attack plant leaves (BBA, hair algae, etc).
It is also known that diatoms require silicates. Tanks have some at the beginning, and eventually the levels drop. But tanks with sand, or if the source water is high in silicates, you may have a more difficult time, and perhaps a silicate remover (i.e. phosguard) will be required.
Finally is it always a good idea to add tankmates that eat diatoms (otos, and/or some types of snails).
My 2 cents... I'm not sure diatoms are really well understood.
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post #3 of 4 (permalink) Old 04-27-2015, 03:02 PM
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The tops of some of the Rotala look good. I also see new growth on the S.R.
Rotala often take a while to get started after planting unless the stems are very long.
I use the calculator to get the EI doses and just do one each week instead of three
because I have no CO2. Seems to work.
The doses for KNO3 is 1/8 tsp in my tank. But I get a test result that is just starting to
turn red with that. So I use 1/32 + 1/16 tsp of the K2SO4 and 1/32 tsp of the KNO3
and this gives me a light Orange...I'd say 10-15 ppm. Tested just before the water change.

The shortest distance between any two points is a straight the opposite direction...
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post #4 of 4 (permalink) Old 04-27-2015, 10:55 PM
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I've been battling diatoms also - from a really thick bloom after a few weeks, to just a light dusting here and there lately. I had lights fairly short too - 5-6hr burst with a few hours sunrise/sunset. As per the link below, I started increasing light intensity and duration, and the diatoms have stopped forming, almost completely. The stuff that was there before is sitting there, but no new stuff is appearing.....

Read down to the diatom bit..... the rest makes interesting reading also....
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