From May till this month I ran a successful 20 gallon long aquarium, which started out with DIY CO2, diffused through an Aquaclear 30 filter. There were two T8 48 inch bulbs, and I varied their height so as not to have any major problem with algae. Eventually I replaced the filter and removed the Co2, and reduced the light. The tank continued to do very well.
Over time, I was gradually moving my plants, filter, and DIY CO2 over to a 29 gallon aquarium, which was set up last October. Unfortunately this 29 gallon aquarium has not done as well as the 20 did. Although the tank was started in October, I have had a problem with diatom algae for quite a while. I believe the problems worsened with this tank when I went from a single 23 watt CFL quite a height above the tank, to the 48 inch T8 bulbs. I also added my DIY CO2 around that time. I've varied the light: sometimes one bulb, sometimes two, sometimes raising them. Today I switched back to one T8 bulb, around 17 inches from the substrate.
The dilemma with light is that plants are not growing very well. On the other hand, the tank is suffering from a fairly mild case of fuzzy algae, which I nevertheless find very unsightly, as well as the ongoing brown algae.
I use an EI fertilizing proportion, but the amount I dose varies. Last week I began raising it to 5/6 of the EI dose, but only an 8-gallon water change (not 50%). I did this because there have been nutrient deficiencies visible.
Valisneria grows well and spreads. Xingu sword does much better than it ever did. However, hygro corymbosa is very stunted compared to what it was in my original tank. Ludwigia repens, which grew wonderfully in the 20 gallon, is now severely stunted, has many potassium deficiency holes, and is about to die away. Bacopa caroliniana grows fuzzy algae and becomes very dirty by collecting mulm in the fuzz. Hygro difformis has become very unattractive, with emersed-style leaves, long internodes, and brown algae. Myriophyllum aquaticum, lovely in the other tank, now grows fuzzy algae.
Here are my theories as to the cause of the troubles, but they are only guesses: The AC30 is possibly inadequate flow for this large of a tank. This might lead to algae. The tank is also very mulmy despite my gravel vacuuming and filter cleaning. I recently added a hydrosponge 2 on an air pump (not good for CO2, I know).
The AC30 may be a poor way to diffuse CO2. The problem may be compounded by the fact that this is a larger tank. I do use two bottles but I think the production varies. So there may be insufficient CO2 for the light. I don't have a drop checker.
My options seem to be either to go higher tech: Increase light to please stem plants, buy a better device to diffuse CO2 and a powerhead or filter to increase flow. Possibly realize a need for pressurized CO2. I don't wish to go this route.
Or go lower tech: Give up on the stem plants that are straining for the light and grow what does OK. Keep only one T8 on top of the tank at about 25-28 PAR. Use the DIY CO2 or leave it off. Keep the hydrosponge for additional filtration.
I would love to hear your ideas. Obviously it's quite sad to have done so well with the first tank (now closed down), then to upgrade and have things go downhill. But maybe it is the nature of the larger, taller tank. What do you think?