FAST-FLOW CLOSED-CIRCUIT MARINE AQUARIUM 



73 



END OF FIRST 

 OR LAST TANK 



Figure 4. — Units for taking water to and from 

 the pump. They are of black Alkathene except 

 for the adapters ^vhich are Perspex. 



gallons of water per hour (370 and 450 

 U.S. gallons). 



This pump has run without fault for 

 over 4 years; its only maintenance is an 

 occasional cleaning (about twice a year). 



It should be noted that the pump also 

 aerates the water. 



The tanks 



The tanks are of normal construction 

 with angle-iron frames and glass fronts, 

 backs, and bases. The one miusual fea- 

 ture is that the ends are of Perspex. Per- 

 spex has advantages over glass in that the 

 hole for the connecting units is more easily 

 made and its greater resilience allows for 

 small expansions and contractions due to 

 temperature changes. 



The glazing cement is made by mixing, 

 as dry components (proportions by 

 weight), 3 parts litharge, 3 parts silver 

 sand, 3 parts of plaster of paris, and 1 part 

 powdered resin, and then adding enough 

 linseed oil to make it of puttylike con- 

 sistency. It takes a few days to harden. 



This cement is inexpensive but not al- 



together satisfactory as it tends to become 

 rather brittle in time. In normal use it 

 is quite sound, but careless handling or 

 jolting of tanks might cause it to crack 

 and cause a leak. 



As is well known, iron frames need very 

 careful and thorough painting to prevent 

 corrosion. Normal oil-bound paint has 

 been used here, but renovation has been 

 necessary every year or two. Epoxy-resin 

 paints would be well worth trying and 

 are likely to resist corrosion much better. 



The dimensions of the tanks and the 

 position and bore of the inlet pipes are 

 of some importance in relation to the main- 

 tenance of an adequate rate of water flow. 

 The tanks here are 3 feet long, 8 or 10 

 inches wide, and 12 inches tall. They con- 

 tain water to a depth of 3 to 10 inches 

 (see "Tidal conditions" below). The 

 cross-sectional area of the tanks is kept 

 small, as this, combined with the capacity 

 of the pump, largely determines the rate 

 of flow of water (but see note on swirling 

 in the next section). 



Tank connecting units 



The pipes connecting one tank to the 

 next, and those connecting the 'first' and 

 'last' tanks to the pump are made of black 

 Alkathene. They are modified from units 

 made commercially for plumbing pur- 

 poses. The details are shown in figure 5. 

 These units were designed so that a single 

 tank may be removed easily from the series 

 for repair or maintenance. A siphon made 

 of the same material is kept in reserve and 

 is used to maintain the circulation should 

 it be necessary to remove a tank. The first 

 and last tanks are provided with a 'bend' 

 (fig. 4) to Avhich are bolted the adapters 

 for receiving the water from, and con- 

 ducting the water to, the pump. In all 

 cases watertight seals are obtained by add- 

 ing a film of vaseline (while the units are 

 dry). 



The connecting units are fitted as near 

 to the bottoms of the tanks as possible. 



