Bob A wrote:

All of my plants seem to be healthy and growing rapidly (at least the
fast-growing ones), except for one. I have had what I
believe is BBA starting about the time of that post.

I am changing 20g water every 4-5 days. I have to use RO water so I add
Kent RO Right plus one quarter tsp MgSO4 to the water I put in. Could the
lack of Calcium (or something else) be the problem?

pH 6.6
KH 3 (this is color-change after 3 drops, NOT before, is that the
correct way to read it?)
Presumably CO2 ~20ppm
Using TMG as directed, except I break it down into the correct amount to
dose twice a week.
110w/55g

I know you want to limit PO4 to control algae, but since I am using RO
water, and no PO4, could this be a problem?

One other thing, NO3 is going down (not just after water changes), when it
gets 5ppm I add one quarter tsp KNO3 which brings it back up to 10ppm.

Reconstituting RO can be tough, speaking from experience. I wish our tap water
weren't semiconductor/agricultural sewage with 30ppm nitrate at the tap!

Here's my recipe for a 72 gallon heavily planted and heavily stocked tank: I
change about 20 gallons per week. My targets are KH 2-2.5 and pH 6.4-6.6. My
current formula per 2O gallons new RO water is:

2 teaspoons Kent RO Right (reconstitutes GH)
1 teaspoon baking soda (sodium bicarbonate) (raises KH)

My weekly fert regimen is:

1/4 teaspoon Plantex + B
1/4 teaspoon K2SO4
3/4 teaspoon KNO3

pH is 6.4, KH 2, yielding 24 ppm CO2 from a bottled source.

Since you are changing nearly 50% of your water every 4-5 days, the simplest
answer is for you to adopt Tom Barr's strategy described he

http://www.aquatic-plants.org/fert/e...st_index1.html

Search the archives of this group or APD for postings by Tom Barr to read his
recommendations. Here's a good one from APD:

http://fins.actwin.com/aquatic-plant.../msg00404.html

Regarding Phosphate, current thinking is that an excess of Phosphate IN THE
ABSENCE OF OTHER IMPORTANT NUTRIENTS will encourage algae. The trick is not to
remove phosphate, because it is a macronutrient after all, but to provide the
other necessary nutrients. Here's a useful post on that one:

http://groups.google.com/groups?hl=e...b1d7e4d&rnum=1