Why won't my plants grow?

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Registered Member
Dec 1, 2002
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First my tank parameters...

72 gallon freshwater
pH 7.2
dKH 10
dGH 16
CO2 (calculated) 19
Nitrite 0
Ammonia 0
Nitrate 40

I am injecting CO2 and have 110 watts of cf lighting. I have two amazon swords that seem to be finally doing well - getting bigger with new growth. My val is not doing much other than loosing leaves and sprouting pale new growth. The hygro I planted was doing OK but is more recently loosing lots of leave and heading for the grave. I have more green algae than I want and everytime I hit the tank with some nutrients, the algae takes over.

1) I sense that my nitrate is too high. Is 40ppm too high? Other than water changes, is there a good way to keep it down? I am changing 30% every two weeks.

2) Is my KH and GH too high? Will this limit plant growth? I have crushed coral in the filter.

3) How can I control the green algae? My otos aren't really up to the job. They are outnumbered.

4) Do I have enough light? My bulbs are 9300K. Would Actinic bulbs be better? Or maybe a mix?

Thanks! :D


Fish?.......What Fish?
Aug 19, 2002
Somerdale, New Jersey USA
Yes, your nitrates are, IMO, way too high. If not the entire reason for the algae out break it is a definite contributing factor.
You need to try to keep the nitrates between 0 and 10 ppm.
Once again, in my opinion, you need to do a 50% water change and keep doing them until the nitrates fall into the above parameters. With your lighting you will continue to have problems with algae until the nitrates come down. It won't hurt to do 20-40% water changes at least twice a week until the nitrates come down. Now you have to ask yourself why they are so high to begin with. Are you over feeding? Are you over stocked?
Which brings up the next question.....why do you use crushed coral? Do you have Africans or some other "alkaline" fish? IMO, the PH you mention is a little on the high side for plants(7.2 is borderline high) and the crushed coral only makes the water harder and more alkaline. So if you don't need to have the PH that high or the water that high, I'd pull the coral.
As to the lighting.....that's not my field....your wattage is good, but there are many who know the ins and outs better than me.
Good Luck


No mater where ya go, there ya are
Sep 4, 2001
Hurst, TX
Your nitrates should be at 5 to 10 ppm. So yes, it is too high.

You dont have enough light to benefit from Co2. You need to bump that guy to at least 2wpg. Preferably 3+wpg. So add another CF light or suplement with something else.

Stop adding crushed coral. You only need to have a 5 kh for pH stability.

What nutrients do you add?


Registered Member
Dec 1, 2002
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I'll definitely deal with those high nitrates. I'll do those water changes and cut back on the feeding. The tank is stocked with 3 honey gouramis, 2 opaline gouramis, 2 pimos, 5 otos, 9 tiger barbs, 2 black finned sharks, 4 corys. Too many??

About the crushed coral... My KH was in about 3 with just my tap water. When I got my CO2 injection going I had trouble keeping the CO2 in the safe zone. I lost a few tiger barbs during one overnight CO2 rise. So I added the coral to raise the KH. It had been around 6 for a while and today it was up to 10. Not sure why. I am planning to take some out of the filter. At 6dKH the pH was varying between 7.0 and 6.8 (DAy to night). I was much more comfortable with that and will try to get back to that equilibrium.

About the lighting... My concern with adding more lighting is the heat. The lights are resting on the glass top and I want them there for asthetics. The water temp is 78-80 degrees and the heater never really comes on. The lights are heating the water. My worry is that if I add more lights, the temp will be a problem.


* * * * *
Nov 27, 2002
Austin, TX
Actinics will not help.

Lowering the KH is probably a good idea, but I do not think it will have that great of an effect on your algae problem.

I would recommend more lighting. If you are worried about heat, add some vents to the lights so that the heat will dissipate from the fixture, or maybe set up a fan.

I would recommend weekly water changes rather than biweekly.

Let us know what you are doing for macronutrients, are you adding N P or K, if so from what source? What about traces? What fert(s) are you using?

What does your green algae look like? It is growing in strands, a slimy coat, spots, coloring the water? Sorting out what algae you have will give a better idea of how to control it.

How long is you photoperiod?

What CO2 system are you using? If you have a canister you can get a solenoid so you can shut it off at night to avoid huge PH swings. If you are doing DIY you are going to have issues with a tank that large.

What sort of filtration are you using?

What sort of substrate do you have?

With that info I think we can better assess the situation.