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Black dots on bulb plants
Grant Miller wrote:
> My bulb-type plants have an ever-increasing number of black dots that are
> hard to the touch and cannot be scraped off.
It's tough to diagnose algae problems from photos, but it looks the way a
lot of algaes do when they're beginning to establish themselves.
> Here are my tank stats for your diagnosis:
> - - 48 gallon community tank with tetras, clown loaches, etc.
> - - no snails that I know of
> - - I have a DIY co2 injector (pop bottle variety)
> - - 1 40w power glow fluorescent light
> - - PH is 6.6, ammonia 0 ppm, nitrites 0 ppm, kH 2, gH 3.
> - - I do a 1/3 water change each week and add 2 teaspoons of liquid plant
> fertilizer at that time (Aquatic Stuff Plant Fertilizer)
> - - I feed the fish only once a day
> - - The light is on from 7:00 am to 10-11:00 pm.
> - - Temperature is 26C or 78F
You don't mention your fish load, but my guess is you've got excess
phosphates in the water column, and the algae that's amnipresent is taking
advantage of them. You don't mention nitrates (just nitrites and ammonia),
but I'll bet you've got zero. The point here is that plants utilize both
nitrates (actually they prefer ammonia!) and phosphates, though only in a
certain ratio (I think it's 4:1 NO3:PO4 and would love to have that
verified). Algae blooms often result from excess PO4, but less often from
excess NO3 (I keep my tank pretty algae-free and it regularly tests at 20ppm
NO3). Therefore we strive to make our tanks phosphate-limited (zero
phosphates with an excess of nitrates), rather than the other way around.
My suspicion is that your tank is nitrate-limited.
If I read corectly (a single 40-wat fluorescent) you've got less than 1
watt/gallon of light, which may be at the heart of your problem (BTW, the
plants aren't able to make much use of the CO2 at this low light level).
Adding another 40 watts would help, but 2.0 - 4.0w/g is considered the
typical range for planted aquaria with CO2. Adding light will increase your
plants' growth rate, meaning you'll have to add more nutirents to keep up.
If I've read incorrectly you've already got 140 watts of fluorescent
lighting, resulting in 2.9 w/gal.
First get your lighting up to at least 2.0 w/gal. Then manually remove as
much algae as is feasible. Lastly check your nitrate levels and phosphate
levels with reliable test kits (don't ask whcih ones, there are entire
religious wars being fought on this very topic). If you've got measurable
phosphates and zero nitrates - and I'll bet that's the case - consider
adding nitrate. The most common form is KNO3, which will provide
much-needed potassium as well as nitrates. If you're indeed nirate-limited
you'll have gone a long way towards minimizing further outbreaks of algae,
and you'll probably see the algae you've got start to recede.
michael at rubinworld_com