Here's an strange sounding tip for reducing the time you spend cleaning algae from the glass: dose sodium silicate to promote a controlled population of diatoms. Diatoms! I know... bear with me
Most aquarist's introduction to diatoms is as an unsightly reddish-brown coating of their sand and rocks in the first few weeks of a new aquarium. At that point, most decide that diatoms are a "Bad Thing (tm)" and are forevermore willing to do anything at all to avoid diatoms or even the possibility of diatoms. When diatoms are out of balance (like that bloom in a new aquarium), they don't do anyone much good. But when diatom populations are in a stable balance with other processes in your tank, they are very good for the whole system.
Good things for aquarists might include:
- Diatoms compete with blue-green algae for resources (#1 reason to mention this here).
- Diatoms are much easier to remove from glass and acrylic and less unsightly than blue-green algae (light gold tint compared to algae's green blotches).
- Diatoms are part of "plankton" and just like plankton products that you can buy, they provide a healthy natural food for filter feeders.
- Diatoms consume nitrates and phosphates from the water column and fix them into their tissue where it can be filtered out of your system via your protein skimmer (don't worry, your skimmer won't get all of them).
- Diatoms on your sand are some of the best possible food for your cleanup crew and are likely to contribute to their longevity and increased health/diversity.
Now, how to get them to grow in balance in your aquarium. Diatom populations in home aquariums are largely limited by available silica. In order to get more diatoms without getting too many diatoms, you need to maintain a low but stable level of soluble silica in your tank water (I seem to get effective results from 1ppm, though I personally haven't tried concentrations higher than 1.5ppm).
Before you dose something, you should know your tank needs an external supply, and you should be able to measure the level to know where you stand. Hatch makes a good kit for measuring soluble silica (detection level is .05ppm). To buy soluble silica, you want to buy the smallest amount of "water glass" you can buy from your local crafts store. "Water glass" is sodium silicate and it is used to preserve eggs (presumably artsy eggs, but I didn't ask). The smallest I could buy from the local Michael's was 1 quart, which is enough to keep an entire club's tanks dosed for several years.
The stuff I bought was 41 baume, which is 29% silica by weight. I dilute this stuff into a quart of working solution so that each teaspoon of working solution will dose 10 gallons to a level of 1ppm. It takes 3 3/4 teaspoons of 41 baume solution to make a quart of working solution, which will treat almost 2000 gallons to 1ppm. (If you've got a tank under 55gal, this is probably too concentrated to be convenient, so you should probably add 1 1/4 tsp to make a 3x dilute solution and use three times as much when dosing). This stuff is very alkaline (even more so than sodium hydroxide -- kalkwasser), so use gloves and clean up well.
Once you have your dosing solution mixed up, estimate your total water volume, which is probably somewhere between 66-80% of the tank's total volume, depending on the density of your rockwork and the depth of your sand. Perhaps a first dose to 0.25ppm, so if your first silica test shows undetectable silica, divide your volume of water by 40 to determine the number of teaspoons to add (divide by 13.333 if you made the "small tank" solution). Always dose into a high-flow area (remember the alkalinity). I suspect that anything up to 1ppm will be fully consumed within a week and you'll probably be at the detection limit of the hatch kit (0.05ppm) within five days. I started out testing every other day and found that I have to dose about 0.33ppm soluble silica each day to maintain a tested level of 1ppm. Now I only test for silica every month or so along with my other water quality tests.
If you don't use RO/DI filtered water, it's possible that your water already contains silica (among other things). You need to take this silica into account when figuring out your dosing regimen, so having and using a test kit is doubly important for this case. Many people who find that they have trouble with diatom blooms are likely to find that their water has very high silica levels: 18ppm or higher. I recommend removing this from your water with an effective filter (RO/DI) to prevent blooms and then adding a precise (and small) amount of silica back to your tank to encourage balance.
As I said earlier, I maintain 1ppm in my main tank, and that seems to be the lowest amount that makes the glass scrapings much easier and the color of the dirty glass more pleasant (I'm lazy and refuse to scrape more often than weekly). I've heard of people having no blooms with levels up to 3ppm, but I do see a dusting of diatoms on my sand every few months (not a bloom and gone within 24 hours, the tiger tail especially loves diatoms) and am unwilling to raise the silica further without a clear reason to do so.
Regards,
Ross
